If one in twenty guys (or more) is a real and true rapist, and you have any amount of social activity with other guys like yourself, then it is almost a statistical certainty that one time hanging out with friends and their friends, playing Halo with a bunch of guys online, in a WoW guild, in a pick-up game of basketball, at a bar, or elsewhere, you were talking to a rapist. Not your fault. You can't tell a rapist apart any better than anyone else can. It's not like they announce themselves.
Shakesville: Feminism 101: Helpful Hints for Dudes, Part 3
That rapist who was in the group with you, that rapist thought that you were on his side. That rapist knew that you were a rapist like him. And he felt validated, and he felt he was among his comrades.