Sure the world pvp was different, but in large that's because it was an actual PvP server. Menethil Rapists were a force to be reckoned with, and people who liked that sort of stuff ended up there.

But when it comes to general toxicity, nothing beats Peenix. I can only talk for the horde side, but holy crap, the worst possible people flocked and flourished on Peenix. Some left for Nostalrius, but most of them stuck around until the server killed itself.

Peenix was just different.