The phrase "ur mom" is well known to be used to do a little trolling or as a come back to an insult
Person: HA! You're a noob!
Funny individual: ur mom lol
A come back or how to answer someone if they want to hang out and u don’t
A: You’re so stupid
B: Ur Mom
A: I-I—
A: Hey wyd this weekend
B: Ur Mom
A: oh ok……Well maybe another time! bye :/
epick burn you tell people when they're being gay
person: you're a bitch
you: ur mom
Ur mom is an insutl than u can use it without ofending any one but its an insult
ur mom is ugly