A STD ratio is a simple acronym for Slut to Dude ratio. This helps when going into a bar and seeing if it is worthy of your patronage. A high STD ratio would mean there are more sluts than dudes, while a low STD ratio would mean the reverse.
Hey bro, I was just in Waterman's and the STD ratio was at least 3:1. I was super stoked. Lets do some G.