ur mom refers as a comeback or a slur to some people. You may use "ur mom" as referring to your actual mom, or you may refer to "ur mom" as a sort of comeback when someone asks you something and you don't really know what else to say besides, "ur mom" lol hehe.
hey ur mom is over there!
hey what's up? ur mom hehe
yo, why are you so ugly? nah I'm not, but ur mom is..
A comeback to win every argument ever.
Person 1: Hey Joe what are you doing tonight?
Person 2: Ur Mom.
Person 1: Hey I have some leftovers do you want some?
Person 2: Nah, ill just have ur Mom.
an expression/"insult"
person 1: "u look stupid"
person 2: "ur mom"
the hottest person you'll ever meet on earth.
Jake: I did your mom so hard last night
Birth: Omg lucky I would totally do a three sum with my mom too!!
A insult/comeback that makes you instantly win an argument.
Guy A: ur mom
Guy B: Dude, using such a cringe, overused, lazy, lame insult that doesn't make me cry? How pathetic, I don't even have a mom. If I did, I still wouldn't be mad or sad. So say all the "ur mom"s you wanna say, I won't give a goddamn shit.