Maybe someone could explain this to me...?

There's this kid in our apartment complex, a young girl, Not sure how old. Maybe twelve...? Anyway one day I was sitting in the apartment, had the blinds open, and was reading a book. Out of the corner of my eye I I see someone move in front of the window, and stand there for a moment. I look up, and this little girl is standing there, dressed like her parents don't care. A small tight shirt and shorts short and tight enough they look like their trying to replace her lags, and she's just smirking at me. It's the look of amused disgust that many full blown teens don't even like to show very much, let alone adults. I attempt to ignore it, go back to my book, but she keeps standing there just looking at me as if she had seen the most disgusting thing ever. I give her a look that says "WTF?!" and she wandered off, but not before I saw her laughing quietly to herself as if I were the biggest idiot on the planet. Than another time I moving some stuff and found an old "Simpson's" cap in a container. She was the only kid outside, and wasn't looking at me. I asked her if she wanted it, and she started to turn with polite interest like any kid would, but as soon as she saw me she simply stopped, and the "Oh it's THIS idiot again" smirk resurfaced. She simply stood there with her hand on one hip, looking me straight in the eye and basically seemed to challenge me somehow. I snapped this time. "Do you want it or not?!" I demanded. She giggled, shook her head, and waved a dismissive hand at me as she walked off again. I don't look or act particularly strange, and had never spoken to this girl or her family. Both times I was fully clothed, (not in boxers or anything) and even had a shirt on. I swear this was the creepiest little child and she pissed me off too. Can ANYONE explain this?