I recently teamed with this guy who promised, promised everyone on the PUG a million Inf if he died, he was so sure. He would run ahead like two, three, four rooms at a time. Plus you can guess what happened to him, multiple times. He ended up dropping out wordlessly, without paying anything. 🙂
Running ahead and riling up mobs without dealing with them yourself is something a jerk move. Despite being careful, it's easy for players behind you to come around a corner only to realize some mobs are standing right there, or worse, running towards them.