lip cousins 

when two people realize they've kissed and/or made out with the same person.

addendum: the closeness of the relationship is dependent on the length of time passed between said incidences. Like, if two people "crossed paths" over the course of a week, it would be known as "lip twins." But if it occurred years apart it would be "lip cousins."

"ashley! i can't believe we made out with the same boy!"
"yeah. we're totally lip cousins."

lip cousins by tengelke October 21, 2012

cousin lip

another word for cleft lip, or harelip.

john: remember sarah? with the lip thing going on?

theo: you mean sarah with the cousin lip ?

cousin lip by ovosalesman March 5, 2023