You all miss the point. mkay, as in the South Park satire, was used by a smug, patronising teacher who says it after a lesson in a tone of fake understanding and empathy with his listeners. Nobody would use it as a substitute for 'okay' except tongue-in-cheek, mkay?
A new legal drug many teens use, like coke it's snorted or smoked and looks almost identical to it, although it's actually good plantfood.
The drug gives a short rush and can affect eyesite, mindset and can make the user feel like shit for the coming days. Best kept for the rubber green plantin the corner of your bedroom.