For me it had to be Hogan at the Bash joining the NWO. I remember watching it live and freaking out. I was 13 at the time, grew up on Hogan in WWF but knew that he gotten STALE as hell in WCW. I never EVER thought he would turn heel. It changed wrestling forever. Of course he got really really TERRIBLE after that and defended the world title like once every 4 months.