Crabs in a bucket mentality. It's not surprising, people in high school are immature when it comes to boys and girls interacting. Boys love to tease especially if they can see it's getting a reaction. Depending who does the teasing just brush it off or hit back.

This is why I find it preferable to do things out of the public eye, people are bound to try and make it awkward if you're doing your initial approach and trying to flirt in front of everyone. Once you've established a connection and you're doing most of your obvious gaming alone in school, or out of school at parties and through DMs/Snapchat, people can't say shit because she won't care.

And also watch how once you're in there and have opened the door, those same insecure and jealous guys will the courage to ask you for tips or use you to flirt with her friends.