A sickness brought on by sleeping with a horribly unattractive person. Usually contracted during consumption of massive amounts of alcohol. The illness leaves the person feeling sick to stomach, dirty, depressed, and unwilling to leave the house.
guy1: Hey wanna ride with me over to the party tonight.
guy2: Nah man I'm staying in, last night I contracted a horrible case of swine flu.
guy1: Yeah I saw you leave with that walrus of a woman.
guy2: You ASS! Why didn't you stop me and give me a back handed flu vaccination before I went and got all sick.