Way before my time but I have heard, pound for pound, Forbes Kennedy was someone many didn't want to tangle with?
https://www.youtube.com/watch?v=V-s6uT16S8A
So many names come to mind. Stu Grimson, the Grim Reaper, The Boogey Man, Derek Boogaard, (as already mentioned) Colton Orr, Brashear, George Leraque, George Parros, Eric Lindros, and of course, Wendel Clark, one of my all time favorite players. Not many come any tougher than what Clark brought.
(Wendel Clark and Joey Kocur are cousins in case some of your didn't know that and that is why they never fought one another.)
Turn this one up!
https://www.youtube.com/watch?v=_7XgYSoK1go
https://www.youtube.com/watch?v=HF3wVJPdAs4