I think you're pretty much talking about the fundamental attribution error. It's a cognitive bias whereby we interpret the actions of others as the result of their character, but attribute our own behavior to external situational things.

I think another component of this is generalisation, like how often does someone have to do mean things to qualify as "an asshole". Once in a lifetime? Once a year? Every day? All day?

I used to think I was a super nice person. These days I will absolutely acknowledge that there are times when people would think I was a bit of an asshole. I think sometimes it's unavoidable if you don't want to be everyone's door mat. For example, when you disagree with someone sometimes you can just let it go to keep the peace, but if you feel strongly about it for whatever reason and have to stand your ground, it's easy to end up looking like an asshole.