smarty pants
1. One who obnoxiously and frequently attempts to assert perceived superiority in intelligence; a know-it-all. Don't be such a smarty pants. You don't know everything.
2. One who makes jokes and uses sarcasm in an attempt to seem witty, but instead is deemed annoying; a smart aleck. OK, smarty pants, are you going to help me, or just stand there mocking me all night?