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The semen left over in a vagina that has slowly made its way out and accumulated around the labia. This semen over time dries and forms a buttery cream.
I went down on this chick and it was obvious that i was getting sloppy seconds the cum butter build up was insane.

cum butter not to be confused with duck butter

If this chick doesn't shower her boyfriend is gonna notice my cum butter.

by Jonathan M, Madison H December 10, 2008