extremely rude; outrageous; utterly insolent
Strongly emphatic, often used in formal or written contexts to condemn behavior as beyond the pale. Combines 不届き (improper, rude) with 至極 (extremely).
Even I felt anger at his utterly outrageous attitude.
Residents complained one after another about the municipal office's extremely insolent response.
Compound of 不届き (improper, rude) and 至極 (extremely). The exact historical derivation is uncertain, but the combination serves as an emphatic formal expression.