A fork of Rural Dictionary
Just about. The greatest comeback to anything. Used mainly when talking about the size of genitals, but can apply to anything else.
Person A - Hey look at our science. That's bigger than yours! Person B - That's not what your mom said last night! Person C - Oh BURN.
A comeback that people say when someone says, " I bet you are terrible at sex." Or other comebacks. Then that person would come back and say, " That's not what your Mom said in bed last night."
Guy #1: Your dick is probably the size of half of a raisin. Guy#2: That's not what your Mom said in bed last night.