Cunnilingul drift 

When, during the act of cunnilingus, the toungue of the performer 'drifts' to the receiver's anus.

"Dude, I was eating my gf out last night, but I wasn't concentrating and got some cunnilingul drift!"

Cunnilingul drift by Fifth Horseman April 15, 2010

cunnilingual drift 

v. When a person's tongue drifts down to a woman's anus, on purpose or by accident, during an intense session of cunnilingus.

Credit: Dan Savage (Savage Love)

"Man, I was so drunk I didn't even realize I was savaging her butthole! It was cunnilingual drift, dude!"

cunnilingual drift by D'emon July 18, 2003