Khloe Kardashian -- Back, Back, Backin' It Up in Vegas

Khloe Kardashain was a real trap queen ... and at least one guy was more than happy to fall into the trap when she put her best assets backward in Las Vegas.

The most recent KK sis to go platinum was at 1 OAK nightclub when a guy -- who seems to be a friend with major benefits -- danced up and invited Khloe to get closer.

Let's just say Khloe, and her ass, are loving the single life.