There are other stories where someone claims something that can't be proven and that was either not witnessed, or must have been denied by everyone. Yeah it sucks if everyone on your team is protecting a douche, but... is HR supposed to intervene and fire someone because only one person claims something happened?
edit: *I mean anyone in HR. Obviously the team members protecting people are at fault in the first place. If you're on the victim side of this, you have to have a paper trail. Even messaging a coworker, "Didn't [boss]'s joke bother you? Where he/she [dropped the N-word | kept talking about sex]?" Then HR investigation can't say there's no evidence. If it progresses to the point of a lawsuit, now you actually have evidence.