Was a toon on Thalia went on for days about raping another players dead mother, the fact she died from cancer and how he should go slit his wrists and join his mum. This abuse went on for hours at a time over several days in World Zone and players Trade channel.
What happened the person being abused quit the game. We see botters running 24/7 for dog meat nothing gets done at all.
That is horrible, and I hope the person who was doing that was finally banned. Well, I hope worse things happened to him than that, but that is outside the game. In game, banning is all that can be done.
That said, you did ask for one case, and that really needs a single example of someone being banned. It was instant, too, not a result of a ticket. Someone with GM power was on and took action right away.
Cases such as you mention can be used to make argument that there is not enough GM pretense, and it would indeed be a good support for such argument. There is a difference between not enough and none.
During the rush of gold botters, there was a system proposed that if enough players report someone as being a problem, that person would be silenced based on those reports, and then unsilenced if investigation proved that he was not breaking rules. Essentially, a way for a group of people to exercise limited GM powers. Essentially, a form of citizen arrest (hope, this makes sense to you, wiki says Australia has similar concept). There were strong arguments that it would be prone to abuse, and in some way it would be. Still, one can design a system that would get creeps like you mentioned off the server right away and leave honest disagreements somewhat safe.
P.S. On personal note, ignoring groupies till they say something of note. Getting less and less likely, though.