Let me just. Spill feels on that bottom gif for a minute.
Look at that. That is just - a perfect reaction, summed up in half a second clip. We can assume at this point, by Loki’s statement “I met them,” that it’s past the point where Loki has thrashed most of the Avengers individually. Even after all he’s accomplished in Midgard, even as he thinks he’s so superior to all of these simple little Midgardians and their primitive lives, that one mention from Tony sets him on edge.
That little annoyed hiss, the head turn, how he bounces the staff in his hand. Look at that. That is annoyance, irritation, insecurity, and anger all bubbling together - and Loki shoves it down, trying to ignore the fact that his brother is here, helping these stupid little Midgardians and their insignificant lives. That Thor ruins everything - he has Asgard, all Loki wants is Midgard, why should he take that away too? That even though he’s succeeded in so much, his brother will always be better than him, and by the Realms he will not let that happen.
It just speaks so much to me about Loki’s inner turmoil - he’s obviously crazypants in this movie. No doubt about that: He’s the villain. But the only reason he get so angry at Thor is because he still loves his brother, somewhere. If he was really apathetic to who Thor was, their history, then he wouldn’t care. But this is thinly veiled bravado, because after all this time, he still doesn’t know how to handle the issues that have plagued him since he touched the Casket. I’m a monster, I may as well act like one.