put a condom
on and have at it. a play on words from the CSI procedure whereby anything that may contain DNA is put in a bag and labeled. In this case, the bag containing the eventual DNA (jiz
) is the condom, and tagging it means to have a go at the pussy
Inebriated guy tells the wild party gal that "he would sure like to get some of that", nodding to her crotch.
She responds: "bag it and tag it", as she first nods to his cock and then to her snatch.