To pleasure the anal cavity of oneself with the intent of sexual gratification.
I really wanted to go down on her last night, but when I got home she was in the middle of an assturbation session to the new Justin Timberlake video.
by decamel August 28, 2013
Masturbation restricted to the ass region. Usually performed by placing dildos, buttplugs, fingers, toothbrushes, or whatever else may be handy into the anal cavity. Lube is optional but highly recommended.
Suzy had never considered assturbation until she overheard Julie talking to Maria about shoving a 9 inch vibrator up her ass while fantasizing about Tom (Suzys dad).
by mindrape November 15, 2005