This EW piece highlights Billy Zabka who played the bad guy (sweeping the leg) in the original movie and the sequel. He also was a bad boy in heaps of 80's movies. And he was wonderful in Hot Tub Time Machine. It is most interesting and impressive that he created a short that was nominated for an Oscar. Not too shabby.
And his sense of humor is intact as illustrated in Sweep the Leg:
See here for an interview with Billy Z.
Of course, to be honest, my favorite part of Karate Kid would not be Billy Z but Elisabeth Shue.