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1.
A toilet muffin occurs when the toilet users ass exceeds twice the diameter of the toilet seat and the ass cheeks hang over the side like a muffin.
Bob: Cathy, how can you tell where your pee is going?

Cathy: I just center my toilet muffin over the seat and hope the cheeks don't hit the floor.
by Nate, Mike & Todd February 09, 2007