Why can't I wear THIS jacket at school?

I would ask your teacher (in private) why they think its inappropriate. It looks fine to me. Its long sleeve, and obviously shows no cleavage. is your teacher a boy or girl? and what kind of shirt were you wearing under it?? and if you're teacher can't seem to answer the question i would talk to a principle or parent about it because its a pretty expensive jacket to not be able to ever wear