butterfingering 

when someone accidentally sticks a finger in their partner's butthole in the heat of the moment.

Did you hear about Lydia? Yeah, Paul's digits slipped and he gave her a good butterfingering.

butterfingering by jessas December 24, 2012

Butter Fingering 

When a women is finger-banged and butter is used as the lubricant. In Australia this may also involve eating the butter off a piece of toast.

"I was butter fingering you after class, It didn't mean we were dating!"

Butter Fingering by HankyPanky420 February 24, 2009