bum your mum
The act of having buttsex with a mother
"Go bum your mum!"
Whatever [bums] your mum.
When someone doesn't have the same point of view as you, you use this saying. Usually used in a sarcastic tone.
"Oh my God! Don't you just love watching hamsters piss!?!"
"Hmm, Whatever bums your mum."
"Hmm, Whatever bums your mum."