This happened many years ago for me. A guy at a party was giving me massive red flags. The final straw came when he outright lied to me and doubled-down on it when I asked if it was true, just to brush it off as a joke later that same day and make fun of me for believing him. I avoided him at every friend get-together afterwards.

A few years later, after I'd moved away, I learned that the rest of the friend group left him too. Turns out he had a habit of trying to hook up with teenage girls and after some event (that I never learned the details of) brought it to light, everybody abandoned him.

God, the vindication felt good.