When somebody on an mmo thinks that they're pro - 'Hero' but they're not, so there is an 'x' on the end. Usually they're the type of gamer that puts others down to try make themselves feel better about being low down on the mmo food chain.
Most frequently males, that try to be cute. However 'Herox' are a rare breed, Troll them while you can.
Herox: Oh I'm so awesome.
Herox: Me failing there was completely intentional, I was just checking how bad you were.