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Your mum in the ultimate come back for anything that anyone says. It originated back in the 2000's when teenagers found that answering questions was just plain boring, so instead, 'You Mum/Mom' became the lazy excuse for everything.
"Excuse me but what are you doing?"
"Your Mum/mom"

"What are you having for breakfast?"
"Your Mum/mom"

"What is your Mum/mom's name?"
"Your Mum/mom"
by Dr Experderatis November 08, 2011