Why would a group of guys stare at you?

Okay here's a bit of background info. I'm not friends with any of these guys, and I sometimes I get stares from one of them even if they're not with their buddies. I know they talk about me because I've seen them whisper and look at me. They go to my school and literally turn around and stare if I walk by. It kinda makes me nervous because I don't know if they're talking sh*t or if one of them likes me?
Why would a group of guys stare at you?
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