noun: a penis that is severely infected with any number of venereal diseases (mostly the worst ones out there like syphillis, clamidia, etc.). A penis that has nasty fluids and puss filled bumps on it and is really the worst thing that can happen to anyone. The reason its called "Vegas Cock" is because not everything that happens in Vegas stays in Vegas (i.e. it comes back with you in your pants).
Coined by A.Ivanov, witnessed by P. Roberts on 8/8/2008
Guy 1: dude i went on a trip to Vegas and fucked a couple a nasty street hookers and I came back with a case of Vegas Cock
Guy 2: fuckin sucks balls dude!