Ha, as soon as I read the thread title I knew tippex would come up.
I bought the paint on tooth whitener and it was literally like thin tippex. You could see the brush strokes in it and where you had missed tiny bits.
My sister bought the extra white one and it was even worse.
Also it says on the instructions that it has to be reapplied after consuming food and drink, so you'd have to starve and stay sober too. (If you were actually going somewhere, alternatively you could look like a twat painting your teeth in the toilet)