Urmom is sometimes also said as yo mama and usually used in jokes or too insult someone or their mom. They have an entire youtube channel on yo mama jokes where you can give them submissions and they will say them in a video if they are new.
Example: URMOM is so fat she is the smash bros stadium.
a different way to use it would be
Example: John: bro what were you doing last night? Joe: urmom.
urmom... . .
Simple and classic insult that never gets old
I hate you
Urmom
Urmom is a fat lady with a bag of peanuts that say suck ‘em before ye eat ‘em.