A. To frolic around acting silly. Possibly touching an erected or flacid member.
B. Goosing is where you're stood behind an unsuspecting victim, you curl your hand in between their legs and grab hold of their genitals.
C. Pinching someone's bum and running away. As in the attack on Sue Turton on Channel 4 News (UK).
Which one?
C is a Jape
B is Rape
A is Drape