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.
Used in the field of criminal investigation and forensics, "bag it" refers to putting evidence in a sealed bag or container, and "tag it" refers to the tag or label attached describing the contents and context of their retrieval. Bag it and tag it can also refer to a body bag and tag describing the deceased within.
They would gather any more possible or trace evidence, bag it and tag it, and take measurements of the rooms.
To bag and tag someone means to literally put a bag over their face and then engage in sexual intercourse (Tag-it). Bag and Tag is used when the person has a smoking body but a really ugly face (kind of like it was beaten repeatedly with a tennis racket). Bagging and Tagging can also work when you are bored of screwing the same person and you place a bag over their face and pretend that its someone else.
Bob "Dude, I'm sooo tired"
Joe "That's not what your mom said last night"
Dude "Dude, my mom is old and ugly"
Joe "Bag it and tag it"