I asked somebody a question, and they said it's stupid(in a friendly manner I hope) and then replied that :"It smacks of the Juvenile"
What does this mean?
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Sign up to join this communityIt means that it has a juvenile (in the sense of "childish") character. Juvenile can have a neutral connotation (it could refer a "juvenile animal" or "juvenile education"), but in this case the connotation is definitely negative (similar to puerile). (Although it may be being used in a playful fashion in this instance.) Juvenile in this case is a "nominalized adjective", meaning an adjective used to refer to the class that shares the characteristics the adjective describes: "the rich" or "the homeless".
In this case, smacks of means "is suggestive of", this figurative use deriving from smack's meaning of "to taste".
I should note that this is a somewhat common phrase (if a touch old fashioned), but it is not idiomatic. Juvenile can be used as a negative adjective in any context. To smack of could theoretically be used to describe any one thing as resembling or sharing characteristics with something else, but it is typically used in an at least mildly negative, or condescending, sense (at least in modern usage).