My seats been taken by some sunglasses
Asking 'bout a scar
He subtly shows his disdain for the man hitting on his girl by identifying him only by his sunglasses (a literary device known as metonymy). Since it’s already dark in the bar, there’s no need to be wearing them; symbolically this guy is useless.
The scar could either be an emotional one, ie. “Are you and him no longer together?” or a physical one, that he’s trying to use to get conversation going. Either way, he’s interested in her.
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