Why does a guy's best friend smirk when he knows his friend likes you?

so the guy who has a crush on me, his friend smirks when he sees me.. and the guy who likes me looks the other way, why does he do this? (the guy who likes me doesn't know that i know he likes me found out from a mutual friend)
Why does a guy's best friend smirk when he knows his friend likes you?
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