Actually, this is an interesting topic - genuine thanks to Tibor.
As far as players on the field, my least favorite was Steve Bellisari; close behind would be Stanley Jackson; both guys really hurt the Bucks with their play.
As far as bad image/attitude guys, my least favorites would be Ken-yon Rambo and Reggie Germany.
Of course, all of the true criminals (Marco Cooper, Andrew Lee, et al.) would make my list.
With regard to Nate Clements ... let's not forget that he had quite a bit to do with the Bucks' failure to win the NC in 1998 - Nate was the genius who let a shanked MSU punt hit him on the leg, which "muffed" punt was subsequently recovered by the Spartans. OSU was leading 24-9 at the time (mid-way through the 3rd quarter), and would have had the ball in MSU territory. Instead, the Spartans took control of the game, and OSU could never get back into it.
Also, I'll always have un-fond memories of Jerry Rudzinski failing to keep containment on the punt which Punk Woodson returned for a TD in 1997.