There are more humans in the world than seconds in your life. Just block the asshole and move on.

I'm noticing a pattern where someone is like "I heard X" and someone says "not true, I have firsthand knowledge" and the first party comes back with "well you would say that, because Y&Z" and the slander keeps multiplying faster than you can refute it.

sometimes I was wrong though

I'm coming here as a bit of a bruised idealist. I can't help but think some people who are acting like jerks could maybe become a bit kinder with a bit of firm but non-assholish pushback.