rusty hook
This is where one person inserts his finger inside his own rectum, as if to cover it in feces, and then sticks it in someone else's mouth and pulls on the victim's cheek, as if the person is being fish hooked. 
On the Jackass DVD 4-Disc Box Set, Jeff Tremaine talks about how Ryan Dunn gave him a rusty hook, and during a photo shoot, you could see feces in Tremaine's teeth. 