Here’s the thing. It could mean many things why a girl would stare at you. Here are a few things out of an infinite number of things why she would stare at you:
You have bird poop on your head.
You have something nasty on your face.
You have stuff hanging from your nose.
You’re wearing something strange.
You’re behaving stupidly.
She’s actually staring at the person behind you.
She thinks you’re familiar.
She’s wondering why you’re staring at her.
She thinks you’re a creep.
She thinks you’re cute.
She thinks you’re someone she knows.
She thinks the poster behind you looks like something she likes.
She thinks the shirt on your body has a message she likes.
The list goes on.
I know what you’re thinking though. You’re hoping that the girl staring at you means something incredibly awesome. It could be, but not necessarily.
One time, during high school, a blond chesty girl stared at me for the entire class. Occasionally, smiling. I found out she was smiling at the hot guy behind me. ^_^