Making fun of someone or something.
A less offensive way of saying taking the piss.
Her prominent eyes swam with tears as she gasped for breath, staring at Ron. Utterly nonplussed, he looked around at the others, who were now laughing at the expression on Ron's face and at the ludicrously prolonged laughter of Luna Lovegood, who was rocking backwards and forwards, clutching her sides.
"Are you taking the mickey?" said Ron, frowning at her.
"Baboon's … backside!" she choked, holding her ribs. -Harry Potter and the Order of the Phoenix
A very British way to ask if someone is taking the piss - ie making fun of you.
Judy - Are you taking the mickey?
George: (with feigned modesty) Shucks, Dick…t’aint no big thang!
Laura: (to George) CLEARLY, you are as dumb as a box of hammers and I would like to kick you as far as I could kick a lemon meringue pie…as usual…Dick is TAKING THE MICKEY OUT OF YOU!
Tony: ‘Fraid not, Dodo-brain girl! George IS the greatest (and cutest president) EVER! Boys rock!
Laura: (exasperated, to Tony) Shut your festering gangrenous pie hole, you putrid tool! Crawl back into the Masterpiece Theatere “Veal Crate” you crawled out of, boneless-boy.
George: (to Tony) Yo, Tony!!! Who’s Mickey?