Peter Quill has ADHD. Sorry, but it's true. I don't make the rules.
He's:
Emotionally reactive (like snapping and punching Thanos)
Listens to music constantly, even while doing important things and especially when he has any free time whatsoever (stimulation seeking)
Afraid of abandonment, i.e his reaction to Ego, feeling threatened by Thor, and his behavior towards New Gamora (Rejection Sensitive Dysphoria)
Comes up with unconventional plans that others are skeptical of, though they actually work, i.e his dance-off with Ronan (neurodivergent thinking)
Works better under-pressure - or rather only works under pressure (first battle scene of GOTG3)
Being overall impulsive
Has fixations/special interest on certain topics - in his case, David Hasselhoff and other forms of pop culture
Stims sometimes, i.e throwing the orb around in GOTG1 and tossing around another type of orb in GOTG3 (that I will not name here for spoiler reasons)
Questions authority and arbitrary rules to the point of being seen as careless or disobedient
He talks so much omg he talks so much, ie. calling people long strings of insults, using talking as a distraction (and surprisingly out of most of the male characters in the MCU) talks to emotionally vent.
He's literally funny in a way only ADHD people can be and im sorry but i mean that ('You're from Earth?' - 'I'm not from Earth, I'm from Missouri.')
He'd absolutely find this list too long to read and would skim it.
