Chunking is the act of shitting for your friend/patient/random tramp by fisting said person in the rectum and pulling the shit out of them. The act may be considered one of generousity but it is sometimes necessay to go that extra mile for a friend.
Tom: "Sure, right after Hannah Montana, I have a mean ass chunker stuck in there."
When someone is too slow to run and not graceful enough to jog, he would be chunking.
Betty was chunking up the stairs because the elevator was out of order.
In many cases, the girl will leave her knickers on for days/weeks in order to cultivate the infection.
She wasn't left disappointed as some bloke was well into chunking, and he went down on her as though she had gold buried inside her