It's a prison thing. Lower inmates are forced to lick the assholes of the leading inmates, but they put salad dressing on it to hide the taste. Hence, tossing the salad.
Noun.
The act of licking the anus and the area between the sex organs and anus, which is covered in a sweet liquid or syrup.
When done in prison, the reciever is dominant; the one doing it is submissive.