I remember when Benitez suffered some kind of broken leg after a flash knockdown against Davey Moore. The referee was waving the fight to continue but Benitez kept looking at the ref and pointing to his leg, so the ref finally had to wave it off. Now that's not exactly saying fuck it, but it wasn't just the ref calling it either.

As for no mas, yeah, that's about the only one that comes to mind where a guy says "fuck it" for no apparent reason at all, no knockdown, nothing. That was a big fight too. Seems to me there was some issue about whether Duran would get paid, I can't remember how that turned out.