I agree with the others here stating that your classmates probably wouldn't care about your keyboard and would only be tempted to look up its details and especially price after you speak about it (some may get curious and ask you about it). Unfortunately, that probably won't go very well for you over the long-run if you have some "problematic" classmates.
Unless you keep it near you at all times, you may risk it getting becoming "lost" (yeah right, more like stolen).
Now in terms of whether you may receive complaints about the keyboard, I think it really depends on what your teachers and classmates are like. Back in the days of my high school, my teachers (for the classes that involved computers) were pretty friendly and had a good sense of humour. If I were to bring in an HHKB, they would certainly view it as a little fun toy and wouldn't mind me using it. It also helps to be at the top of the class (an A student with a good personality) as teachers leave you to do your own thing.
I had my fix of rowdy classmates, but the majority of the class was perfectly harmless. It helps to be friends with them.
But I still probably wouldn't bring a keyboard to school. Reason: It lacks utility. You attend your classes, do your lessons, and then you leave. School isn't really enjoyable in the first place, so what's the point of using a fancy keyboard to make yourself feel better?
Similarly, I recalled when some students brought in their laptops for English class, but soon dropped that idea. I tried it once myself. Laptops lacked utility, and it was overly risky lugging around a laptop in a school filled with teenage students. Nobody cared whether their classmates brought one as they felt that they were just trying to show off.
Anyhow, let's all agree on one fact: High school doesn't matter.
