In the Thor movie:
- Loki plans the original incursion of Jotunn into Asgard as a practical joke, and possibly as a sideways minor reproach to his father for paying too much attention to Thor's big day (possibly this has been the only damn thing people in Asgard have been talking about for months, so Loki's well and truly gotten sick of the subject).
- His prank backfires, and becomes much more serious than he originally intended (the first sign of his chaotic nature surfacing) when the Jotunn make it as far as the armoury and almost succeed in walking away with the casket.
- He's present for the argument with Odin, but doesn't realise or recognise that it's his presence which makes this argument much more vitriolic than it otherwise would have been. However, he sees the potential for another object reproach to Odin through encouraging Thor to sneak off to Jotunheim.
- It's pretty clear that Loki's actual objective was to have Thor and the gang stopped before they actually left Asgard in the first place - that's why he told the guard where they were going and what they were doing, with the object that the guard would immediately tell Odin. However, again, Loki's chaotic nature is interfering in his plans - and the plan goes awry when the guard takes much longer to tell Odin than Loki had been counting on.
- Loki probably didn't plan on going to Jotunheim in the first place, which is what Heimdall is needling him about when they first speak (Heimdall's first words to Loki are basically telling him they're not dressed warmly enough). Heimdall is also well aware of what's going on, and probably of what Loki is expecting to happen.
- Heimdall doesn't trust Loki. Loki is the only person on Asgard who can disappear off his radar on occasion. If you're used to being able to see everyone and everything (and therefore not having to trust anyone anyway, because trust implies a certain lack of knowledge) being expected to take it on trust that the one person you can't observe isn't being malicious is a Bad Thing.
- Between Heimdall's instinct not to trust what he can't observe constantly, and Loki's unconsidered chaotic nature, the decision to go along with Thor rather than stalling long enough for the guard Loki primed to get to Odin and get the whole business stopped is a lot easier than it would have been. Plus, there's Heimdall's honour as the gatekeeper to be considered - he wants answers, and he wants to be able to clear his name.
- So, Loki winds up on Jotunheim, and unbeknownst to himself, he's back on what should be his home turf for the first time in his life since he was taken from the temple by Odin (it would be interesting to know which temple it was that Loki was lying in, and which god he'd been intended to be dedicated to - also whether the sacrifice he was presumably meant to be had been completed or not). This is probably the key event in Loki's life which really kicks the chaotic, discordian, trickster side of his nature into full bloom.
- Loki's "damn" when Thor is taunted is sincere and heartfelt. Just when he thought they'd be able to get away without blood being spilled, and without anyone getting hurt, some loudmouth in the Jotunn camp has to insult Thor's manhood, and oh gods, it's on for young and old. The boost Loki's chaotic side has received by returning to Jotunheim is also partially to blame for this - his plans are unravelling almost as fast as he can make them here, and he doesn't have the time and the wherewithal to make better ones.
- Discovering he's not affected by the Jotunn in the same way that his friends are is frightening for Loki. Nobody thinks well when they're frightened, so his ability to think fast and plan on his feet is also hindered here.
- By the time he gets back home to Asgard, he's been scared half to death and in fear for his life, he's angry with Thor, he's bewildered and shocked by this new strangeness about himself he's discovered, and he's definitely not thinking straight. His mental abilities are also probably a lot stronger than they've previously been, and they're certainly a lot stronger than anyone around him is expecting they'd be. This is probably why the argument between Odin and Thor goes so very wrong so very quickly, and winds up with Thor being stripped of his power and exiled. This isn't something that Odin would have done in his right mind (and I suspect this is where Odin, at least, comes to realise that something is wrong) and it's a major strain on Odin's system.
- Loki's next major shock is discovering he's Jotunn, and that he was effectively taken from Jotunheim as a trophy, in many ways. He's not what he was raised to be, he's not who he was raised to be, and he's just discovered that the whole competition he was engaged in was rigged from the start (since, as he rather sagely points out, there's next to no likelihood of a Jotunn being acceptable on the throne of Asgard). The realisation that he's actually a Jotunn prince probably isn't much of a comfort - Jotunheim is a dying world, and is therefore very much the booby prize in this competition.
- What isn't said here is just as important as what was said. What isn't covered is which temple Loki was left in (these things can be very important, after all) and which powers the Jotunn were beseeching for assistance. Laufey was a besieged war leader at this point, and it's likely he was far more interested in finding allies against the Asgardians than in whether or not the particular allies he was recruiting were a Good Idea or not. So we don't know which deity-level figures Loki was intended to be given to. We also don't know whether Loki was intended as a sacrifice or a gift (that's another important distinction as well - if he was intended as a sacrifice which wasn't completed, he may still have Someone or Something out for his blood; if he was intended as a gift, the dedication may have already been completed, in which case there's issues of theft by Odin to be considered). My guess is that the deities Loki was being dedicated to were chaos beings, that the dedication had already taken place (and as such Loki was tainted by chaos) and that as a result, Laufey wasn't going to throw a huge tantrum about his son being taken from the temple. Let Odin have the raising of the boy - it'd come back to bite him in the bum later.
- Odin falling suddenly into the Odinsleep is very much a product of Loki's chaotic influence (it helps for Loki if you think of him as the walking embodiment of Murphy's Law - around him, if there's two ways of a thing happening, and one of them will cause chaos when it happens, that's the one which is going to be more likely to happen. He basically warps probabilities to a fine old fare-thee-well). However, Loki genuinely cares about Odin, no matter how angry with his father he may be. So he does try to do the right thing, even though his very self is warping that right thing around him to be the wrong one.
- Quite honestly, the two pieces of genuine malice Loki exhibits in the film are the deliberate mis-information of Thor, telling him that their father is dead, and that their mother doesn't want to see him (and this can be explained as Loki basically wanting Thor to feel as isolated and homeless as he suddenly does) and Loki's sending the Destroyer to kill the Warriors Three, Sif and the entire population of the small town in New Mexico where Thor is hiding out.
- Loki wants to be respected, he wants to be liked, he wants to be appreciated. This is why he does a lot of what he's doing. He's destroying the Jotunn not only as a way of cutting the diplomatic Gordian Knot he wound up creating with his brother, but also as a way of destroying that which he hates about himself. His besetting sin isn't malice, however - it's pride. He's too proud to accept second place.
Tags: