The act of Pooping on a toilet and Masterbating at the same time, with the goal of simultaneous climaxes of both pooping and masterbation. remember Poosturbating is not just a mans activity.
Timmy S. was in the bathroom for a long time, we heard moans and he had his computer with him. He'll never admit it but judging by his relaxed manner afterward everybody concluded he just finished a poosturbate session.
To use poo as lube while masturbating.
My palm went dry, so I crapped out a quick one and just finished it with a poosturbate.