when someone fucks ur mum they say ur mum to tell you that they fucked ur fat mum.
ex:
them: 'what did you do'
you: 'ur mum'
she is not real. you where adopted. But hey, at least they wanted you. :)
Fake Mother: Yo, child. I aint ur mum fam.
Child: Ok boomer
When a salty kid on any game platform or in rl has no comebacks and is probably very special.
You: Bruh get that outta the game ur so bad even god couldnt submit.
Him: SHUTUP, UR MUM!!
Typically used by 12 year old British kids with elite humour. Used as an insult
Person A: What are you doing?
Person B: ur mum 😎