Is sticking your tongue out immature?

Well in school, high school, someone stuck the tongue at me. I don't even know her, so i ignored her. But in the inside I was like WTF. She looked like a freshmen or sopre, I don't know. So do you think its really immature for a high schooler to stick the tongue at you? I wouldn't care if a 5 yr old kid did it to me. But what would be your response if someone who supposed to grow up already stuck the tongue at you?