The semen which seeps out of the anus of the female counterpart after anal sex has been initiated. The mix of feces and sperm (and occasionaly with the addition of lubricant) create a dairy like spread that goes great on Wonder Bread.
"No fool, I aint feelin dat. Lets get some toast."
"But i aint go no butta"
"Foo, iss aiight, cuh ima put it in yo mamas boo boo and make some butter."
"You mean like boo boo butter?"
-Willy Wonka & Charlie