Guys, How does a guy indicate his level of interest when he meets a gal?

Inspired by @Ladieman94's question: Do most guys not see when girl flirting with him?

What's the difference between the ways you treat a gal you want to befriend vs a gal you hope to take out and have a relationship with (vs a gal you think is just good for a one night stand)?

Guys, How does a guy indicate his level of interest when he meets a gal?
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