IPA: /ɪmˈpɜːtənəns/
KK: /ɪmˈpɜːrtənəns/
A rude or disrespectful act or remark, often showing a lack of respect for others.
His impertinence during the meeting shocked everyone present.
Impertinence is formed from "im-" (meaning not) and "pertinere" (meaning to pertain or relate). The word describes behavior that does not pertain to proper conduct or is not relevant, hence it signifies rudeness or lack of respect.
Think of 'not pertaining' ('im-' means not and 'pertinere' means to relate) to proper behavior — that's why impertinence refers to rudeness.