A sling fuck is a supporting black leather cradle that is strapped, hoisted to the roof with chains, which a person is able to lay back on, and wait to be sexually penetrated. See Bondage or Mistress.
A sling fuck is a dirty term used for promiscuous men and women at sex clubs that like to be fucked by lots of multiple partners. See slut or cockworshipper.
"Yeh I sling fucked that slut from the ghetto last night."
"Excuse me Miss Vanstone, would you be interested in a sling fuck tonight?" "Should I order the tip truck to slide you in?"