Reflecting on the thread subject, I thought about what the dirtiest things that I ever did. Mostly some headbutting against those I didn't really like from the tie up position. That one was pretty common from others too. One that was a little less common, and would give me a good callous on the bottom of my chin, was just digging my chin deeply into the opponents back and spine to cause him to squirm. Taught to me by a sadistic assistant coach when growing up.
Last year, the "dirty wrestler" of the year seemed to be Mantanona and his strangle move. Zahid also used that in world team trials.