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The eating, drinking, or ingesting of something by way of the anus.

Sometimes the insertion (but not consumption) of objects into the anus may also be referred to as buttsumption.

A term that usually accompanies anal sex with a very loose anus. The extra flaps of moist skin form a seal around the penis, acting as a plunger and sucking it inwards and onwards, deeper into the abyss.

The butt seems as though it is swallowing the penis whole.
Mark: "Hey dude, you ever had a beer enema? Gets you drunk like mad crazy!"
Paul: "Think I'll pass on that one."

Hannah: "Stuffing my bum with acorns."
Jack: "I don't think those are meant for human buttsumption."

Tom: "Hey Bro, heard you got anal from Alice last night?!"
Jerry: "Yeah. Too bad her anus was loose as a clown's pocket. Her butt almost swallowed me whole!"
Tom: "Damn, dude. Sounds like a case of penile buttsumption!"
by Angrywank March 17, 2013