I worked in an office and overheard a young girl on the phone with a customer. I heard her say 'well I don't know nothing do I?' I exchanged horrified looks with a colleague. When she got off the phone I said to her 'thats a double negative' she said 'huh?' Well I said 'if you don't know nothing then you must know something' I got 'huh?' again and at that point I gave up. That was back in the 80's so it doesn't look like things have changed much.
Bev x