Guy 2: What about TK?
Guy 3: Yeah man he donked too but it was nothin' on Jimmy's donk.
Origination: It is the short-hand for donkey, which is of course a synonym of ass through animal nomenclature.
Other: The term became exceedingly popular after Soulja Boy's song by the same name was released.
Boy 1 (pointing) : She got a donk!
Boy 2: Damn dude, she does have a donk.
Denning: You shoulda brought a gun instead of a beer, mate.
Nugget: Nah. I don't need one. I got a Donk.
Denning: Got a what?
(Crocodile Dundee II (1988).