noun. A keen, ass-specific, eyeball-detecting sense.
Related terms: gaydar, straightdar, bi-dar, loserdar, jailbaitdar, moron-dar, sexual-geniusdar.
Real citation: "There will be hot chicks. And while they are running, hot chicks are too focused on their splits and/or music to realize their "someone is staring at my ass"-dar is going off."
("Operation Stop Being Fat," May 6, 2004, http://nattysci.com/displaypost.aspx?Post=45)
Made-up citation: "I need buttock-augmentation surgery. I want to be noticed. I want my someone-is-staring-at-my-ass-dar to go off like a car alarm from hell!"