When two men of dubious sexual orientation practice the art of homosexual sex. The fact that they are not confirmed homosexuals, means this is just a little experiment, that they can later put down to doing a bit of "stunting"
Often men who are ragrded as very tough or very cool, will indulge in some recreational bum stunting without the knowledge of any of their friends. Bum Stunting is prevelent in most male macho activities, for example, boxing, shooting, motorcycle riding, wife beating, mountain bike riding and more. It can also be used as a term when something painful happens to your rectal area.
"Wow the boys are so macho, no one would ever guess that they all go and Bum Stuntin in the sheds after practise!"
"I really have a thing for mountain bike riders from hornsby, but I am a little concerned about them as I have heard they like to practice the art of Bum Stunting"
"Rob got thrown off his Mountian bike the other day and got smashed in the ass by his bike, I think it was trying to Bum Stunt Him..."