During male on male gay anal sex, the act of "reaching around" and giving your partner a handjob. This action is considered common courtesy and must be performed unless your partner specifically requests otherwise. Failing to do so is punishable by law in Montana, South Dakota, and New Mexico.
A courtesy reach around is the opposite of a "Spite Reach-around," in which the receiving partner is given a reach around despite specifically requesting to to have one.
While John was plowing his man-lover in the asshole, he decided to be polite and give a courtesy reach around.
I bet your the kind of guy who fucks a man in the ass and doesn't even have the goddamn courtesy to give a reach around.
-Gunnery Sergeant Hartman, Full Metal Jacket