Faux pas

A faux pas (French: false step; pronounced foh-PAH) is a violation of accepted, although unwritten, social rules.

Faux pas are very culture specific; what is considered good manners in one culture can be considered a horrible faux pas in another. For example, in America it is usually considered good manners to bring a bottle of wine when coming to someone's house for dinner. In France, however, this is considered insulting, as it implies that the hosts can't provide their own good wine.

See also: most common Wikipedia faux pas