Sick Rat

Most commonly used in Australia. Can be used as an insult to anybody, but generally laid off at your friends or acquaintances in a jokingly manner.

Can also have the potential for appraisals, such as another Australian colloquialism fully sick('fully sick, mate' after can be used as well).

"Your such a sick rat."
OR
"Your such a sick rheeet" (emphasize on the rat to show even more disgust)