Taking the Mickey

Irish slang

Taking the mickey out of someone.
To tease, make fun of someone, fooling someone, Almost always meant in a light-hearted way.

"Taking the piss" means pretty much exactly the same thing.
"Take the mick" variant, is more often used in the UK.

"Ah sure, I'm only taking the Mickey. I wasn't serious."

"What? Please tell me you're only taking the mickey?"