smarty-pants /ˈsmɑɚtiˌpænts/ noun Learner's definition of SMARTY-PANTS
[noncount] informal + disapproving
: a person who talks and behaves like someone who knows everything自以为百事通的人；自作聪明的人 -
Go ahead, smarty-pants, tell us about your grade point average.说吧，百事通，说说你的平均成绩是多少。
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Don't be such a smarty-pants. [=know-it-all]别以为你无所不知。