Rudeness (also called effrontery) is a display of actual or perceived disrespect by not complying with the social norms or etiquette of a group or culture. These norms have been established as the essential boundaries of normally accepted behavior. To be unable or unwilling to align one's behavior with these norms known to the general population of what is socially acceptable is to be rude and are enforced as though they were a sort of social law, with social repercussions or rewards for violators or advocates, respectively.

Rudeness, "constituted by deviation from whatever counts as politic in a given social context, is inherently confrontational and disruptive to social equilibrium". Rudeness, particularly with respect to speech, is necessarily confrontational at its core.

Forms of rudeness include acting inconsiderate, insensitive, deliberately offensive, impolite, obscenity, profanity and violating taboos such as deviancy. In some cases, an act of rudeness can go so far as to be a crime, for example, the crime of hate speech.