smart alec
colloquial noun phrase

- someone who tries to appear clever or who answers questions in a clever way that annoys other people

Cambridge Advanced Learner's Dictionary

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According to G.L. Cohen, author of Studies in Slang Part 1 (1985), the phrase smart alec (sometimes written aleck) stems from Alec Hoag, a famous pimp and thief in New York City in the 1840s.

Hoag, his wife Melinda and an accomplice known as French Jack operated a deception called "the panel game" in which Hoag's prostitutes robbed foolish customers. The rooms where the women took their customers had sliding panels that enabled Hoag to sneak in while the customer was asleep and steal their valuables.

Before Hoag created this trick, a prostitute's accomplices would wait until the customer was asleep, then burst into the room. But the customers eventually got smart and would block the door with a table or chair propped up under the doorknob, thinking they would then be safe. However, "Smart" Alec Hoag never woke the victim and would be on the other side of town before he knew he had been robbed.

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SYNONYMS

know-it-all, smart-ass, smarty, smarty-pants, swellhead, wise guy, wise-ass, wisenheimer

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Practice OWAD in a conversation:

"John is a brilliant programmer, but he can be a bit of A SMART ALEC from time to time."