that's the sound your mother made last night
originated from SNL when sean connery said it to trebek. can be used to any sound that could be sexual.
Trebek: What sound do dogs make?
Sean Connery: Moo
Trebek: No.
Sean Connery: But that's the sound your mother made last night!
Sean Connery: Moo
Trebek: No.
Sean Connery: But that's the sound your mother made last night!