The fluctuating dilation of the anus after a traumatic event, that makes it reflect the differing sizes of the British 50 pence and 20 pence coins (both coins are hexagonal).
Phone conversation.

Friend: "What's up man?"

Sufferer: "Dude, I've eaten nothing but white bread for three days and I've just had my first shit."

Friend: "Woah, nightmare!"

Sufferer: "Tell me about it, I've been curled up on the couch for the past hour and a half sucking my thumb while my ass is all '50p 20p'."
by Rydo December 20, 2010
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