9. Loki Stabs Thor (Avengers: Assemble)
During the Chitauri invasion of Earth, which Loki is megalomaniacally leading, he encounters his brother Thor and the two battle atop of Stark Tower. Thor gets in close and highlights the destruction going on in New York all around them and asks Loki if he really thinks this madness will end in Loki's rule. At first, Loki appears to repent, sounding regretful as he says it's too late to do anything about it. Thor, falling for the act, says they can do it together, at which point Loki exploits the break in the fight and cowardly stabs Thor while he is vulnerable and offering to help. They fight a little more (or should I say Thor beats down on Loki some more), before Loki cowardly rolls off the building on to a passing Chitauri flier and retreats.