Impertinent, cheeky, or arrogantly bold—used negatively for someone (often younger) acting disrespectfully toward others.
そんな生意気な口をきくんじゃない。
Don't speak so cheekily.
あの子は生意気だけど、仕事はよくできる。
That kid is cheeky, but he does his job well.
年上に対して生意気な態度を取るのは失礼だ。
It's rude to be impertinent toward someone older.