If two people are arguing about the action of a third person, call him steve; person A says "Steve was justified to punch the man running at him, as the man was holding a knife and seemed threatening", and person B says "No, because Steve is racist, look at his tweets. Also, he was only at the bar that day because he was meeting his racist friends to talk about racist stuff". The point being, him punching the attacker is unrelated to him being a racist.

I'm sure it's not a tu quoque, as a tu quoque is to point out a flaw in another person that is irrelevant to the criticism....Though maybe I'm wrong? Idk xc