Girl's Behavior

Girls, Why did this girl pretend she didn't know me?

A couple years ago I was interested in a girl who was surrounded by her friends. I engaged the group but only the group leader seemed to want to talk and didn't give anyone else space to talk. Since I was interested in a different girl I just stopped talking. The group leader let's call her K, started starring at me when we were on the bus. She asked me one by one if I found each girl in the group attractive. To each I replied "she's ok", she got really pissed when I told her that I was into her friend and not her. She proceeded to call me names and I just ignored her laughing it off. When I saw her in school she made an issue over my moustache since she didn't like it. Saying "It's not Movember so shave it". Again I laughed it off since I liked the attention but not her.

I later started seeing her wearing an obvious push up bra, which didn't go with her figure.
Eventually I stopped seeing her in school, and went to university.

Today I saw her at a party. Well actually she saw me first since when I walked in and started talking to my cousin I saw her standing next to her friend talking and pointing at me.

Eventually I was able to walk up and talk to her. I asked if I knew her from somewhere and she nonchalantly responded that she'd never seen me before.

Why did she act like this?
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Girls, Why did this girl pretend she didn't know me?
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