My friend wont stop touching me and its freaking me out

For Context We are both 16 year old straight males and I don't really even know him that well. He's just in a lot my classes so we talk pretty decently but recently hes started to grope my chest and thighs and its really freaking me out. He's tight with the teacher in the class too so he doesn't really face any disciplinary action. I'm not tryna report him but how do I make him stop; I've seen some people talk about how they like yell stop touching me but just looking for advice if any of ya'll have faced this.