Base Breaker: He's...a bit of a touchy subject among wrestling fans. On one hand, it's hard to argue with the fact that he's a hell of a talent. On the other, there's a lot of resentment over the fact that during his first run, he had (in the words of CM Punk) the keys to the kingdom handed to him and just walked out.
Narm: During his contract signing: "This is real, John. This is a real feeling that you're feeling, because I...can FEEL IT!" Brock set a record for most uses of the words "feeling" and "real" in an episode of live action television on that night.
X-Pac Heat: Brock Lesnar's background in pro wrestling is constantly mocked and decried by his detractors.
When he defeated perennial fan-favorite and UFC Hall of Famer Randy Couture the crowd was solidly against him and roundly booed him during the post-fight interview.
Then there was the infamous post-fight rant after his second bout with Frank Mir in which he attacked a major UFC sponsor and concluded with the now-immortal, "I might even get on top of my wife tonight."
↑before he missed it at Wrestlemania XIX and suffered a concussion as a result