Well I don't think it is disputed that John Ruiz is one of the most disliked fighters of the era for two reasons.

(1) He clinches ALOT and this is percieved by many to 'ruin' fights. and
(2) He gets many title shots and to many (in undeserved fashion).

Oddly enough I don't mind Ruiz that much and think he did quite well for his god given abilities. I don't really mind clinching as some do but will admit that clinching is a part of Hatton's arsenal.

In short, everyone likes to pick on Ruiz either because they hate watching him, they hate his ability to get title shots, and the fact that he has been on the recieving end of one of the quickest knockouts in history (Ruiz/Tua).