Often a baldfaced lie used to sueak out a couple of extra paid days off; employed to extend a long weekend, travel to an out-of-state Wednesday night rock concert, stay in bed all day with a new romantic interest, etc. Most people would rather come to work sick and risk infecting their colleagues than give up an illicitly obtained and healthy day of fun.
"Where is catherine today?"
"I saw her making out with some douche bag Lastnight maybe she took a sick day to get laid"
"The format: three young lads are put in a house for two months trying to catch as many diseases as possible. The producers want them to be infected by nits, lice, flu, sexually-transmitted diseases and warts, rather than things like Aids and cancer which aren't quite as much fun. A doctor will be on hand to ensure they don't get too ill."