Acting overly clever or crafty in a petty way; sly, pretentious or impertinent (usually negative).
あの子は小賢しくて、先生の注意にもすぐ言い訳をする。
That child is cheeky/too clever in a petty way and immediately makes excuses when the teacher reprimands him.
小賢しい言い回しでごまかそうとしないでください。
Please don't try to cover it up with clever-sounding excuses.
彼の小賢しい態度に周りの人はうんざりしている。
People around him are fed up with his petty, smart-alecky attitude.