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.
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?'