Well I'd have to agree on the past prime Tyson shenanigans
Holyfield has had a long-standing reputation, (although I've not seen enough examples of it), of dirty fighting
I don't know about worst of all time, (as in consistently commiting fouls), but I've noticed Felix Trinidad lose a point in more than enough fights for hitting below the belt that it couldn't be just an accident in my opinion.
Zab Judah seems to me to be someone who is nasty in the ring.
I forget which one these guys stated outloud that they see nothing wrong with dirty doings, but both Jose Castillo and Joel Casamayor seem to try and get away with as much as they can.
Nadel Hussein against Manny Pacquiao used almost ever trick in the book.