Your mom was an old school classic of a come back and might me still ro this day. But do NOT use if there mom is dead or if they want to forget there mom. But it is still a joke so don't tack so seriously.
gad damnnnnnnnn he almost as fat as your mom
calling some one an idiot and saying that your mom does "bad things"
I bet that is not what your MOM said last night
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
A comeback
Jane: "You know who else suffers from dementia?"
Bob: "your mom XD"
Jane: "kys"