foundlingmother

General
Loki eats. He eats a lot. He's not a messy eater the way Thor can be, but he eats. People assume he doesn't because his plate is always full. Loki's especially partial to meat and fish (*whistles innocently*). He enjoys rich, bitter dark chocolate and wine. Extremely sweet foods overwhelm him.

Loki's ambidextrous.

Loki smells like various bitter/sharp-smelling herbs (the scent of his bath oils and soaps) and books.

In private, Loki can be quiet physically affectionate with specific people with whom he feels comfortable (Frigga and Thor, for instance). He enjoys being touched by those same people, though, in public, he might pretend it's a hardship.

Loki suffers from mental illness. Depression is one aspect of this, and this accounts for why he tends to dwell on the negative. His memory is very good, but it's especially good at recalling painful moments. Comments Thor made that wounded Loki ("imagined slights" and "know your place" will never be forgotten). Slights against him. The times when he searched for pride in Odin's expression and found none. "Your birthright was to die." Good memories exist, perhaps even in abundance post-IW, but Loki always struggles to escape his most painful memories. When they're not consuming his thoughts, they loom at the edges of his mind.

Loki is a hoarder. He keeps his surroundings fairly neat (aside from papers and haphazardly stacked books), but he stores so many things in pockets in space, and he doesn't clean those pockets out... ever. It's full of books, clothing, jewelry, spoils that Thor brought back from hunts, old weapons, a pouch of seeds, tapestries, various trinkets Loki purchased in Asgard's markets (he's a magpie–they collect lots of stuff, not just shiny items). There are centuries worth of items in Loki's storage.

Loki adores children. Sometimes, in the wrong mood, they can grate on his nerves, but most often he finds them endearing. They're imaginative, easily enthralled, and... they can be cruel, but not in the way adults are. They don't mistrust Loki for not adhering to societal norms. They're curious, if they notice Loki's differences at all. Loki performs magic for children, enjoying their awe. He amuses them by making silly faces at important events behind the backs of other, more serious, adults, or by carrying out spectacular pranks. He tells stories (often about Thor), exaggerating parts to entertain and omitting the genuinely frightening elements (a little fear's good, but too much causes nightmares and insomnia). He spells their daisy chains into a state of permanent freshness. He animates inanimate objects to behaving in ridiculous ways. He's just good with kids. Kids love him. (Then, to Loki's dismay, they grow up and become dull and/or scornful.)

Loki sleeps curled up. He likes to be surrounded by pillows and heavy comforters, nestled deep into the mattress. Loki alternates between sleeping so deeply that no one can wake him and sleeping fitfully/not at all (often for days at a time).

Pre-Thor
Early Childhood:

When they were small, Loki often pretended to like the same things Thor did. Classic little brother trying to be cool by mimicking the older. This is something Loki grew out of naturally, as many little kids do, but he also grew resentful of the fact that Thor’s interests and skills made him actually cooler than Loki.
Loki didn’t get why Thor needed other friends.
When he was very young, Loki didn’t ask for his hair to get slicked back. He had a very curly head of hair. Thor liked it a lot and was sad when Loki started greasing his hair up.
Loki loved to pull pranks. Sometimes they were more cruel than funny, but most of the time they were harmless.
Baby/small child Loki had the sweetest smile and laugh. He smiled and laughed a lot more, especially with Thor and Frigga. Thor made it his mission to make him happy as often as possible.
Thor and Loki played dress up in their mother’s closet. Loki sometimes stole pieces of his mother’s clothing or jewelry (a scarf, a necklace, a pair of shoes, etc.). He thought they were beautiful. Frigga let him keep some of it, and those items are in a pocket dimension when Asgard’s destroyed (I refuse to accept everything precious to them is gone–Thor has some stuff on Midgard, and Loki’s got stuff in pocket dimensions).
Loki lied about having nightmares or being scared of the dark so that Thor would fuss over him/snuggle with him.
Loki mostly taught himself to read. Frigga helped a little, but Loki was too enthusiastic to wait around for someone to teach him.
Loki loved creepy/scary looking stuffed animals best. They were confiscated after he began to transform into the creatures they represented. A maid walked in on Thor playing with a baby bilgesnipe, and a whole wing of the palace was up in arms before Thor managed to explain it was just Loki, and what’s the big deal? Yeah, he’s nicked me a few times, but that’s just part of the fun!
Loki sits and watches Frigga get her hair done and apply her makeup. He learns to do it by observing, and helps her style her hair frequently. In the privacy of his own chambers, Loki does his own makeup.

Mischievous Childhood Actions:

The usual stuff. Soap that turns hands or hair different colors. Ruining meals by swapping sugar for salt (or more creative food and drink mix-ups and mayhem).
He used illusions to make the maids and kitchen staff think there were bug or rat infestations.
He enchanted doors to make very loud, obnoxious noises when they were opened. Sometimes foreign dignitaries would come and doors to banquet halls would be screaming all the time. When Odin would make a grand entrance into the throne room, Loki would enchant the opening doors to sound like mating bilgesnipes.
Loki sends glitter-bombed missives to Odin's advisors.
Odin mentioning the goat not belonging at the banquet table? That’s something Loki did (with Thor’s help–Thor thought of using a goat). Through illusions and potions, Loki had one Lord convinced he was courting the most beautiful woman in all of Asgard, but it was a goat. He brought that goat as an escort to one of the parties at the palace. Odin wasn’t nearly as amused as Thor and Loki.
Loki steals Thor’s educational tomes and seals them away in pockets of space. This gets their tutors very frustrated with Thor. (On the Statesman these come in handy for teaching the surviving children.)
Loki transforming into Thor and the two of them talking in unison or confusing someone by seemingly being in two places at once. This is, for a while, how they welcome new guards or maids: by creeping them the fuck out until they learn Loki’s a shapeshifter (look, they’re both little shits, ok–Thor laughs about the snakes).
Releasing the horses from the stables and leading them through the streets of Asgard, much to the distress of the stablehands.
He’s used magic to explode the public baths like geysers.
Loki used to transform himself into a raven (despite a magpie being his preferred avian form) and watch people in Asgard to make them uneasy because they thought he might be Huginn or Muninn.

Valkyrie is not the first person to call Loki "Lackey" (though she's the first to say it to his face). Thor often became absorbed in his training and would forget to eat or drink. Loki would bring him food and water (and admonish him for being such a fool). On one such occasion, Loki overheard other young warriors laughing, referring to him as "Lackey". Thor's lackey. Loki never attended Thor again, though after a few months he mentioned Thor's habit in a casual, not at all concerned way to Frigga. She saw to it that Thor didn't forget to take breaks to see to his body's needs.

Loki learned at a young age that most people found rigorous academic research and analysis/critique painfully boring, so he stopped trying to talk to people–Thor especially–about it. Loki knew that Thor wasn't really listening when they would sit in the library, Loki reading aloud. It felt invalidating to have no one who he could talk to–who wanted to listen–though he still treasured those days where Thor wanted to sit and be in his company in the library, even if he was ignoring the words coming out of Loki's mouth.

Loki’s perception of his appearance is rather complicated. Due to his tendency to dwell on the negative, there are days when he looks in a mirror and documents flaw, after flaw, but, for the most part, it’s not about finding himself unattractive. Rather, it's about something being wrong. He’s not masculine or imposing enough. He doesn’t look like his family. He’s the black sheep. He is hyper-aware of the ways he isn’t Thor. So, he slicks his hair back when it’s naturally curly. He wears shoulder pads. He conceals what’s off, what’s different about him. The wrongness he feels is exacerbated by the body and gender dysphoria Loki experiences. There's never a moment where Loki feels right in his skin, only less uncomfortable, and it has nothing to do with his attractiveness.

Circa Thor
Loki turning the Bifrost on Jotunheim results in the deaths of approximately 3,000 Frost Giants. The Bifrost's blast does not expand, but it causes seismic activity that collapses Jotunheim's icy surface. The blast is sustained for five minutes (300 seconds). I decided that every second about ten Frost Giants perished, putting the number at 3,000.

Post-Thor
Loki is terrified of space after falling into the abyss. He becomes agitated without stimulation–without something to focus on.

Loki struggles to look in the mirror. Even if he knows he’s looking drop dead gorgeous, there’s a hideous monster underneath.

Circa TDW
Loki survives due to Kurse's blood on the blade. It regenerates Loki's damaged tissue, but it scars horribly. It's a hideous, poorly healed scar that continues to cause Loki pain if it's handled roughly or struck.

Circa Ragnarok
Sakaar is full of various species lost to their respective homeworlds and collected there. I imagine the Grandmaster facilitates communication between them, but the translator's rather basic. Loki's Allspeak, which allows them to hear their own languages in the proper accent and with specific word choices or phrases that are very familiar to them, is a fascination and a treat, and it's an element of what expedites Loki's rise within the Grandmaster's court.

Loki fears Thor is dead, so he willingly spends significant periods of time on Sakaar under the influence of dangerous recreational drugs in order to avoid confronting that thought. There are moments when he hallucinates pre-Thor Thor and believes himself to be younger and on Asgard.

The people on Sakaar laugh at other's misery and trauma. That's why Loki tells the story of his suicide attempt. It engages the sadistic audience, and makes him appear one of them.

The Mind Stone altered Loki through exposure. That's how Loki's able to access and manipulate memories. This ability does not extend beyond accessing, obscuring, or forcing others to relive their memories. He cannot alter the substance of the memory. So far Loki's used this ability on Odin (he seals away/fogs Odin's memories and places him in a care home on Midgard) and Valkyrie.

Loki knows the Space Stone will not be destroyed along with Asgard. He grabs it. It doesn't occur to Loki that Thanos will come to retrieve it himself. Loki expects that Thanos will send pathetic minions after him. People Loki can kill or manipulate. Thanos showing up in person is unexpected. It ruins Loki’s plan (to keep the Infinity Stones away from Thanos–that's about the extent of the plan).

Circa IW
Broken necks don't kill people instantly. Loki knows it will kill him, so he releases his life force to protect Thor. That's how Thor survives long enough for the Guardians of the Galaxy to arrive.

Post-IW (Alternate MCU Universe)
Loki keeps busy with projects. One of these projects is to begin to rebuild Asgard's library. He saved many books because they were stored in pockets of space, but they're the only copies now. Loki doesn't like reading e-books. (Stark knows this and bugs him by buying him a Kindle for “Asgardian Christmas”–”Yule, Man of Iron. Do not be purposefully dense.”) However, he appreciates the technology because it offers him another avenue to protect the depleted written sources of Asgardian culture, history, etc. For subjects that Loki doesn't have tomes on, he speaks to experts (or the survivor who comes nearest to that title), and transcribes their knowledge.

Another of Loki's projects is to rebuild the Bifrost. Jane Foster assists in this endeavor. The work well together when they're in agreement, and their arguments are explosive when their calculations do not match. Loki respects Jane's intelligence, and tells Thor she was too smart for him.

Loki's the worst sort of person to allow on the internet. He creates multiple false identities to mock/torment the Avengers on social media, Thor in particular. He covers his tracks too, so even if the Avengers suspect, they never know for sure that any account is Loki.
He doesn’t generally catfish in online dating–even pretending to romance mortals is beneath him–except for one time with Banner. When Thor finds out what Loki’s done, he genuinely does not want to speak to him or be around him for a while, and Loki seethes because Thor will walk out of the room when Loki tries to rile him up. He knows he must do the unthinkable and apologize. Tony has Friday record it, and he posts it to social media. Thor has to protect Tony from Loki's wrath, but he can't stop Loki from hacking Tony's account. Tony ends up needing to do a press conference about his recent tweets.