Rivalry and trash talk are a part of boxing, but every once in a while the tension or dislike between the two fighters is real, and usually there's one who you really shouldn't have pissed off, but it usually ends up in classic performances, some examples are

Oscar De La Hoya- he usually was a cool headed guy who wouldn't talk trash and have a pretty smooth press tour, but on two occasions his opponents took it a bit too far and paid dearly, first up Fernando Vargas, with his claims of being "more mexican", that Oscar had a padded record and was well a pussy

http://www.youtube.com/watch?v=XSyLQmTa-HI

even a juiced up Vargas couldn't back up his talk

then came Ricardo Mayorga, saying he'll make Oscar his bitch, and then take his wife

http://www.youtube.com/watch?v=U7PMU7hldfw

proving you shouldn't fuck with DLH lol

Julio Cesar Chavez-in 1993 JCC was still undefeated and had about 80+ wins under his belt including wins over Edwin Rosario, Hector Camacho, and Roger Mayweather, but well that wasn't enough for Greg Haugen who insisted that Chavez only beat up "taxi drivers", and (Haugen) kept fighting that the fight shouldn't be in Estadio Azteca (Mexico) cause according to him most Mexican's couldn't afford the tickets, Chavez told him "you've run your mouth enough and i'm going to punish you worse than you've ever been in your life" and he delivered

http://www.youtube.com/watch?v=Kxu8frKEB8E

can anyone think of any other examples?