The worst kind of sexually-transmitted disease you can possibly get.
It's a mixture of Gonorrhea, Syphilis, Herpes, and the Clap.
It is also customary to clap once when somebody says this
Man 1: Dude, that girl is a total slut...she freaking gave me Gonnosyphiherpeclap.
Man 2: *Claps hands once*
Man 1: What the fuck was that for?