clam bumping 

the act of to women (lesbians or bi) having sex by bumping there vagina's against eachother.

dude, i caught my ex and my mom clam bumping last night

clam bumping by juneaus November 6, 2004

Clam Bumping 

The illusory idea that homosexual women may have sex by bumping one female's vaginal labia against another female's vaginal labia. A slander. Other forms: clam bumper(s).

"Those dikey chicks are off to go clam bumping."

Clam Bumping by Spud January 27, 2004