British love to make fun of and tease each other and that’s exactly what ‘taking the mickey’ means. You can also say ‘take the mick.’

Example: “Stop taking the mickey out of your brother.”

Meaning

Tease or make fun of.

It is sometimes reported that the phrase originates as a variant of the slang phrase 'take the piss' and the the 'Mickey' refers to micturate. This seems rather fanciful and there's no evidence to support that view. It is now more generally accepted that the phrase came about as rhyming slang. 'Taking the piss' does play its part as the rhyming slang refers to a (yet to be identified) character called Mickey Bliss. So, 'taking the piss' became 'taking the Mickey Bliss' and then just 'taking the Mickey'. An early citation of the longer form 'taking the Mickey Bliss' would be useful here, but I've not come across one.

Taking the piss is reported as originating in the UK in the 1930s and 'taking the Mickey' probably came not long afterwards. The first form of the phrase in print - as 'take the mike' - comes from 1935, in George Ingram's Cockney Cavalcade:

"He wouldn't let Pancake 'take the mike' out of him."