smarty–pants 
/ˈsmɑɚtiˌpænts/ noun
/ˈsmɑɚtiˌpænts/ noun [noncount] informal + disapproving : a person who talks and behaves like someone who knows everything
▪ Go ahead, smarty-pants, tell us about your grade point average. ▪ Don't be such a smarty-pants. [=know-it-all]
▪ Go ahead, smarty-pants, tell us about your grade point average. ▪ Don't be such a smarty-pants. [=know-it-all]
