Tea bag is a slang term for a sexual act in which the male puts his scrotum into his partner's mouth over and over. It is called "tea bagging" because it is like a tea bag being put into a cup of hot water and dipped. Some people would not like being tea bagged, but it does not need to be painful.
Tea bagging has been used during hazing or bullying incidents. Groups hold down victims while somebody "shoved his testicles in [the victim's] face" or puts his "crotch to his head."