Guy's Behavior

If a guy nudges his friend as they walk by a girl?

Three guys who I once caught staring at my body head down as I walked towards them. Let's call them A, B and C.

Last time, as they walked by, A whispered to and nudged B who was next to him who nudged C.
But after A whispered to B, he looked at me and noticed I was already looking so he put his head down but he was still looking at me.
B tried to nudge discreetly C, glancing at me at the same time.

Why did they do this? Also, why would you (if you were them) have done this?
If a guy nudges his friend as they walk by a girl?
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