What 's exactly smart-ass means and when would it be necessary to implies it to a person
I've got a weak English yet so I would mind correcting me ,thanks fellas.

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Answer

"smart-ass" refers to someone who knows more but who is not at all modest and will talk about something not commonly known to people who don't know it.
Depending on the situation and the intonation it can be an insult or a joke. If you mean it as a joke it's best to smile!