One of my favorite moments (or two moments), which isn't even a big pop off or anything, is Peter Quill learning that Ego gave his mother cancer on purpose, and then without hesitation, without letting him say anything or monologue, just blows him away, fires everything at him. Because that's what Peter would do, that's his character.
Which then leads to the dreaded moment when the exact same thing happens with Thanos while they are trying to extract the Infinity Gauntlet from him while under hypnosis. Because that's what Peter would do, that's his character.