Timothy Bradley is my own personal definition of that particular phrase. Despite his obvious technical brilliance and grace, i can't imagine anyone 'out-dogging' JMM.
Right now? I'm going to have to go with Brandon Rios that dude has an insane chin and tolerance of punishment.
Lucas Mathysse Provodnikov Bradley Kirkland (he's coming for you, whether his chin holds up is another question) Guererro (against Berto)
margarito. if he were a pitbull, he wouldve scratched until he died. he'd be dead game pitbull. there was just no quit in the man.
The young hungry Morales is definitely worth a mention, just about any version of Erik to be fair but especially the prime version.
Currently fighting, or all-time? Currently, Rios & Bradley definitely need to be dusted for fleas. I'm told that Mago literally sleeps out in a junkyard. Mailmen won't come to his front door. All time? Guys like Frazier, Castillo, Benn & Marciano had been known to actually chase cars down the street & bite the hubcaps.
Rios Lucas Provodnikov Bradley Kirkland Omar Nino is a lesser known fighter, but he won, lost, and drew with Brian Viloria. He's an evil little **** who loves a tear up and only follows the rules when the mood suits him.