When you pull your cock out of an ass and you stick it in that persons mouth the liquid that forms from the act of blowing creates a tan substance and the blower makes a muffled sound due to having their mouth full.
My girlfriend came home with muffle butter on her breath...that hoe.

Jacqui tried to talk but she had a mouth full of muffle butter.
by Jaxtastic August 22, 2015
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