Used to describe a sex act that some people find very disturbing.

Both the man and the woman start out naked. The woman allows the man to put ~1 pint of whipping cream into her anus. The man then wraps a doritos bag around his penis and uses it as a condom.

The man then proceeds to fuck the woman anally while wearing the doritos bag condom as protection. This continues until the whipping cream has been churned into butter.

The butter can then be put on toast or used in another sexual act.

Pour hot butter all over a dildo, then turn out all the electricity, sneak into a girls room and plunge the dildo in and out of a girls vagina like you are churning butter.

The female equivalent to the masculine phrase indicating a level of arousal commesurate with "get his dick wet. In this case, in reference to being the recipient of (penetrated by) a phallus during or for the sole purpose of sexual intercourse.

Penetrating a colostomy bag, instead of the anus, because it's unavailable or you're just that sick.

When a woman is rides a man reverse cowgirl; he grabs her by her neck and hair; and loops her up and down in a circlular motion on his cock.

The result of walking after one has not defecated completely. This is usually due to constipation where the poop breaks in half, and one could wipe all day and still not be completely clean.

When a man ejaculates within a woman's cooch and proceeds to continue humping away even though she is filled with his population porridge. The rod/thrusting action is very similar to how the people (in the days of yore) churned butter.
The fact that spooge is white and creamy, similar to cream prior to it being churned into butter, just adds to the greatness of this term.