A phrase that is easy to describe on urban dictionary because everyone has used it.
1: Dude, there's like a million definitions for "your mom" on urban dictionary.
2: Your mom.
your mom is a modern youngster "joke" with the kids
What did you do last night
Youngster : your mom
the person i railed last night
person A: where were you last night?
person B: why don't you ask your mom
Your mom is a comeback that you say when you have nothing else to say even if it doesn't make sense
Guy1: You're fat and ugly
Guy2: Like your mom