Describes someone, especially a younger or lower-status person, acting in a way that is irritatingly bold or disrespectful. Often used in the phrase 小癪なことを言う (say something cheeky).
That kid talks back cheekily.
Don't get impudent with me.
Usually written in kana; the kanji form 小癪 is rare and may not be recognized by all readers.
Kanji form is uncommon; mainly encountered in older texts or for stylistic effect.
The word is a compound of 小 (small, petty) and 癪 (irritation, a fit of anger). The exact historical derivation is uncertain, but it likely developed from the idea of something small that causes irritation, extending to describe impudent behavior.