When someone does you a favour but you have no intention of paying the favour back. So you're essentially using them as a slave.
Dude, can you do us a favour?
Yeah, what are you going to do for me?
Nothing
Come on, im doing you no slavours
A slightly prolapsed anus that resembles the short trunk of tree stump.
"Dude I was going down on this girl and I noticed her ass hole stuck out like a nipple!"
"Mate that's sounds like some mad, trunkage"