Why would a girl cover up her butt when walking in front of a certain guy?

That has happened from a couple different women, on different occasions. They would walk in front of me with they're hands over their butts, like they're were trying to shield their butts from my "pervert stare".

They seemed creepy, stuck up and rude, and I felt like they're were implying I was a pervert, so I stopped talking to them and instead, avoided them. But when I started ignoring them, they immediately started staring and talking to me.

instead of making me want to talk to them, it just made me confused and weirded out. Why would a girl do that: try to cover up her butt and shield it from a guy's view, then later start staring after he starts ignoring her?
Why would a girl cover up her butt when walking in front of a certain guy?
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