A way for guys to express how they feel about a woman's looks. Usually used to express really ugly women. Its kind of like saying they are really good at looking bad.
Guy 1 - Hey man you have to take one for the team tonight!
Guy 2 - You have to be crazy buddy, those chicks are down with the sickness!!!
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).