
Impolite
Cultural Variance
What's impolite can differ across cultures; some gestures or phrases may be offensive in one place but not another. 
Subtle Signals
Sometimes a tone of voice or facial expression can make a phrase impolite, even if the words are not rude by themselves. 
Accidental Rudeness
You can appear impolite without intending to, such as when speaking a new language and misusing phrases or expressions. 