What's not a sign someone's an asshole, but is often misinterpreted as one?

Massive one. People automatically assume those who have defined areas that others are not allowed to access (ie personal/physical contact, topics of communication, literal areas they restrict in their home, etc) are prudish and being willfully obstinate for unfounded reasons, without considering why these boundaries are set in the first place.

The second you inconvenience someone, they assume you're the problem.