What is a slightly flirty way to compliment a guy's appearance?

There's this event coming up that my crush has to dress up for. I know he's likely going to approach me at the event looking snatch, what's a good way to compliment him? I was thinking of maybe doing a jaw drop and saying "You look so good!"

I need something that signifies that he turns me on a little bit but at the same time I don't want it to seem like I like him too much. Maybe just smiling and giggling then saying he looks good? I don't know what do you guys think?
What is a slightly flirty way to compliment a guy's appearance?
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