I know that test animation inspired this HC and I totally see why it's popular but personally, I see him as less of an "I have anger issues guy" and more of an "I've been wronged for so long but feel as though I don't have any right to be angry about it so I'll lock my feelings in deep inside and let it rot" kind of guy.

I think he keeps his anger to himself, simmering in it silently and letting it wash over him, or expressing it through his stories, but rarely having outbursts. (I'm totally not projecting)

It's sorta the same thought process I had when drawing that angry Bruno sketch, I see him as sensitive and just the tiniest bit emotional (I mean cmon he writes about romance and heartbreak, of COURSE he is). He isn't a stranger to annoyance or frustration but doesn't actually get angry oft. When he does, though, his emotions overwhelm him completely and just. pour out. a broken dam, in a sense.

Also! To go back to the dialogue in the test animation, I don't think Bruno fully shares the "I feel as though the world owes me" sentiment but rather, he doesn't expect anything in return, he'll suffer for the people he cares about BUT what he does get in the end (Mira getting him out of the wall and back to the family (+ bringing light into his life)) would make him feel like it was all worth the trouble.