What was once poor usage becomes standard as the language evolves. The OED gives this gem from 1548: "Muche parte of the common people were therewith right well satisfied." If I am not mistaken, right around 1550 someone complained about this newfangled spelling "much", and demanded that these kids and their slang knock it off immediately. So it goes. And now I'd better 23-skiddoo, chappies.
Sounds to come from the same stable of "End of" at the, er, end of a sentence, meaning nothing other than what we used to say as kids, "so there". I call it the oral version of two fingers.
My bugbear is the trend for people who want to make a negative statement do so by making a positive statement the suffixing it with the word NOT, e.g. "I had a great time out last night, NOT."