"If you feel uncomfortable asking that kind of question or if you're concerned that you won't get an honest response, tell them you're gathering data for a study or something."
Tell them you're a student actor trying out some character traits. The character you're playing is supposed to be a bit annoying or unlikeable. Ask them how you went in portraying those traits.
I wouldn't lead the question by telling them that you were supposed to be annoying, because then they will look for things that annoyed them about you that they may have not noticed otherwise. I would tell them to be brutally honest, and, to be honest, if you're wearing the 'suit' of someone else, you could just ask them if you seemed like the kind of guy they would hang out with. Then note their response down in a survey like manner.
You really should just try asking a close friend, family member, co-worker, classmate, or anyone you spend (or used to spend) a lot of time with (in a friendly capacity or otherwise). That said, the fact that you're asking HN rather than a close friend, family member, etc. suggests that doesn't work for you, for whatever reason.
So try this: go to a random meetup, chat with a stranger for 15-30 minutes, and then ask them if there's anything about you that seems off-putting. If you feel uncomfortable asking that kind of question or if you're concerned that you won't get an honest response, tell them you're gathering data for a study or something.
And if that doesn't work, you can always schedule an appointment with a professional therapist.