You have a crush on Scott but Stiles is your brother, so when your both walking through the halls, he tries figuring out who your crush is

Stiles: “I can keep a secret!” You: “Can you?” you whisper in his ear You: “I like Scott” not even two minutes later, Stiles goes to the stairs where Scott is and sits next to him

Stiles: “Dude! My sister likes you!!” Scott: “that’s ni- WAIT WHAT?!!”