Masturbating while taking a duce. The masturbatory equivalent of a blumpkin.
It is unknown if the word originated as a portmanteau, or if it simply came about as an accurate description.
Me: Oh god what did Jim eat?
John: I have no idea, but he sure is making a lot of noise...
Jim: Oh sorry guys, I'm just doing some blasturbation in here, I'll give a courtesy flush. You should try it yourself, it's pretty great!