What the hell is wrong with my sister?

So I guess I suck at diagnosing most conditions but anyways my sister is making lots of strange sounds of all types right now. It gets especially bad when she brings over her immature high school friends. She's like squealing, yelling, screaming etc. They're having conversations but my sister and 1 of her 3 friends make weird noises while talking. My sister constantly jokes around about autistic people. I also notice teenagers at my old high school keep throwing the term around so casually as if it were slang for "dumbass". What's the deal with these teenagers? Someone with autism wouldn't make fun of other people with the condition.....would they? She has never been diagnosed before but perhaps she has a mild(super mild) form of it? Its either she has Autism herself or she's really immature. I hope she's just being immature. She's probably just being really immature, after all shes only 15 but still...I'd like her to mature some more cuz I don't want her to be around people who have a negative influence on her. I just hate how she mimics people with autism.