To engage in sexual congress, to make the beast with two backs, to be at one with your lady friend
Me: Well mate, did you get the skinback last night?
Friend: No Hommes, it was hot tongue, cold shoulder, I was not cleared for a fly by!
To engage in sex after making cuts on your penis.
"Did you fuck that hooker bareback?" "No, I took it up a notch and rode skinback." ^5