To rile, mock, or be a jerk to another person whether or not the person is joking or being serious.
I know what I am so don't take the piss.
Don't worry about him hes just taking the piss.
to mock someone
"He's taking the piss out of you"
To tease mercilessly or in such a way no one would believe you or to treat someone badly in order to get what you want.
1. (British & Australian very informal) to make a joke about someone or to make someone look silly (often + out of ) They always take 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.
To greedily demand an unreasonable effort or price.
"My physics prof makes us go to 2 labs a week, and half the time we just end up using them to help him mark papers. He really takes the piss."