It's now often used when people take liberties and don't care about the consequences, for instance someone living in a nice house and trashing it or ridings roughshod over neighbours, knowing he won't get evicted by the authorities.
Now he's taking the piss. He had his music cranked up again last night and parks in our parking space.
To appear serious, but actually meaning the opposite - most of the time. Usually followed up by the 'piss taker' (the one who joked) revealing he/she was only joking.
'Hey did I ever tell you you're fucking pug ugly?'