Someone who is constantly posting/linking mean stuff on your facebook wall.
Guy 1: Did you see that mean stuff that chick wrote on my facebook wall?
Guy 2: Yeah man, what a facebook asshole.
Guy 1: Yeah dude, I bet she eats a lot of hot lunch
Someone who is always mean or rude on facebook, regardless of how they are in real life.
Kevin, for how nice of a person you are, you are a facebook asshole real talk