take the piss
1. (British & Australian very informal) to make a joke about someone or to make someone look silly (often + out of ) They're always taking the piss out of her because she's a Barry Manilow fan. 'You should wear miniskirts more often - you've got the legs for them.' 'Are you taking the piss?' (British & Australian very informal!)
2. (British & Australian very informal) to treat someone badly in order to get what you want Four pounds an hour is taking the piss. ￡50 for that old thing? That's just taking the piss.