I had to post this some time -- it's my favorite of the several youtube videos illustrating Tom Lehrer's "New Math". This one includes all the surrounding patter:
Actually, the "New Math" presented here is the way I was taught subtraction, and it isn't too bad. It's nothing compared to the "New New Math" ...
From Tom Lehrer's wikipedia entry:
Lehrer has said of his musical career, "If, after hearing my songs, just one human being is inspired to say something nasty to a friend, or perhaps to strike a loved one, it will all have been worth the while."