A gaffe is a stupid or careless mistake, for example when you say or do something that offends or upsets people. He made an embarrassing gaffe at the convention last weekend. social gaffes committed by high-ranking individuals. = blunder
If you blow the gaffe or blow the gaff, you tell someone something that other people wanted you to keep secret. an embarrassing mistake made in a social situation or in public = faux pas (GAFF)
1. to put one's foot in it, put one's foot in one's mouth, make a tactless or embarrassing mistake. 2. to upset the applecart, ruin something that was going fine