Don't be a jerk and a punk If not as a matter of honor, then as a matter of self-preservation. Pull crap like this, act as if bringing the game into disrepute doesn't matter, and you'll wind up at the bottom of a ruck that means business. And not everything that goes on will come from the other side. Mark L
answer says it all: i never teach my players anything dirty. if you need to do it, you would never play for me.
Tripping, spitting, pulling hair.
I wouldn't really say its dirty, but its most certainly a trick. When there's a ruck n the opposition r trying to rip the ball from 1 of your players, put your right arm past his head, across his chest where his ribs r and twist really hard n really fast to the left. This may seem confusing, but it works
How about.... looking a man directly in the eye and then smacking him? Oh wait, you need balls for that.
Ralgex/deep heat on your hand to wipe in the eyes of your opposite prop at the first scrum.