extremely rude; most impolite
A strong, formal expression used to condemn behavior as utterly disrespectful or beyond the pale. Often found in written complaints or formal reprimands.
His attitude is extremely rude.
Such a demand is most impolite.
Compound of 失礼 (rudeness) and 至極 (extremely, utmost). The combination intensifies the meaning to 'the height of rudeness'.