Why do guys purposely walk by girls?

I notice this happening a lot; I'll see someone from afar and they'll suddenly come up beside me, or walk past me multiple times, stuff like that.

Do they like me, or are looking for a way to break the ice?
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+1 y
Could they just be friendly? Sometimes I know the guys in question, but I don't say hi because I'm shy.
Why do guys purposely walk by girls?
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