For celebrities, Twitter is a double-edged sword. On the one hand the service allows famous folk to continue being famous by pushing their famousness more thoroughly onto the people who consider them to be famous. On the other, the close proximity Twitter grants the famous and the fans can sometimes backfire. If a celeb does something that's considered taboo, dumb, or ridiculous, they can all but expect to be send a barrage of criticism by any of Twitter's 100 million users. Lately, however, some celebs have gotten fed up to the point where they've been firing back at their haters. And it's usually hilarious. From A-list talent to washed-up athletes, indulge in the 25 craziest celebrity Twitter fights with fans.