To engage in the activity of sex, not to enjoy it but to use said activity as a weapon to piss off your ex or to gain from it or to use tactics to gain sex from someone who would not normally have sex with you because it's morally wrong.
Bear Snagging is when two people take a sausage (colloquially known as a "Snag" in Australia) and insert it into the rectum of both parties, while they are both on all fours in the doggy positon and facing away from each other, with the arse cheeks against each other and 50% of the sausage in each person butthole. The idea is then, when the signal is given, to both start "bearing down" on the snag, the objective is to try and shit the snag into the other person butthole.
I was bear snagging my girlfriend last night and lost. Now I've got a sausage in my asshole