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Technically yes it is, but it is definitely not in common usage. Some people would argue that because it isn't in common usage, that it isn't an idiom.
Possably so, in which case it would be a similie. Though truely, an idiom is a phrase from which you cannot gain an understanding without something more than the literal definitions of the words.
In this case, that something more would be the knowledge that a live audience laughs a lot.
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