One of the funniest "most-embarrassing-moment" stories I've come upon in a long time was about a lady who picked up several items at a discount store.
When she finally got up to the checker, she learnt that one of her items had no price tag. Imagine her embarrassment when the checker got on the intercom and boomed out for all the store to hear: "PRICE CHECK ON LANE THIRTEEN, TAMPAX, SUPERSIZE."
That was bad enough, but somebody at the rear of the store apparently misunderstood the word "tampax" for "THUMBTACKS." In a business-like tone, a voice boomed back over the intercom: "DO YOU WANT THE KIND YOU PUSH IN WITH YOUR THUMB OR THE KIND YOU POUND IN WITH A HAMMER?"