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A large, girthy, oddly proportioned, circumsized penis, that resembles a delicious Costco muffin, particularly their coffee cake muffin due to a crusty exterior. This term has also been used in reference to various other Costco muffins, such as their blueberry muffin, poppyseed muffin, and double chocolate muffin. Either way, the chances that it will fit, even into the widest of sluts, is highly unlikely.

These are very common and should be taken very seriously, so if you see one please remember they aren't dangerous (usually), and everyone needs a good fuck every once in a while. So take self medicate with some Rohypnol (Ruffies) and bend over!
DAYUM!!! He had a massive, crusty, Costco Cock Muffin in his pants! It tasted like the real thing!
by Jonsuckscockadoodledoo July 09, 2014
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