What's the difference between a guy checking out a girl vs a guy being nervous around a girl?

Which girl is he more attracted to? Like for eg you check out/ogle girl A but

when you're about to see girl B you take a whole of time to fix your hair, appearance, and are constantly aware of your appearance around her. Also you keep staring at her for long periods even when she's not looking as opposed to just ogling her.

What's the difference between a guy checking out a girl vs a guy being nervous around a girl?
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