I read all the responses and am left thinking "what a bunch of shit." so now i have to responsd and educate like i always do.
Back in the early '90s, MC Hammer did a Pepsi commercial. At the end of the commercial after taking a dramatically long swig from a can, he looked directly at the camera and said with his catchy MC Hammer smile and head shake, "PROPER!" This act was a verbal indication to those watching the commerical that Hammer was pleased with the Pepsi and that it tasted good. Since it sounds gay to give something it's "propers," it has since been shortened to its monosyllabic form, "props."