When you are having doggy style sex and you stick your index finger into your partners ass, then thrusting your poop stained finger into your partners nose and hooking it at an angle, the pulling back screaming "Whos The Baldwin Now Bitch!!"
"My girlfriend was being a bitch all day. When we got drunk later that night, I stuck my finger in her ass while i was ounding her and pulled a "Rusty Hook" on her! Afterwords to finish eairlyer fight I screamed my victory call, "WHOS THE BALDWIN NOW BITCH!?"
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.