It'd never work where I live (medium-sized UK city). I's been said you could walk into town on your hands and nobody would bat an eyelid. People here usually keep themselves to themselves in public places. And if you got really abnormal, you might attract the attention of the police, and I suppose after explaining they'd just let you go. I presume you're in the USA, maybe it's different there, but I can't see how it would be possible to get the reaction the teacher wants, I would think getting public ridicule would be quite hard because I can't imagine strangers volunteering their opinions of other strangers' behaviour, it if weirded them out they'd probably just feel uncomfortable or scared and try to escape in case the weird one was dangerous.
I think it's rather insensitive of the teacher to try to make people put themselves into such a humiliating situation anyway, assuming it worked at all, unless the students were all very ableist and totally ignorant of how a person with mental differences from the norm might feel. I think most ridicule comes from similar jerks who have nothing better to do than to put others down. It sounds like either the local people are mostly jerks who love mocking people, or the teacher just thinks they are. Some teachers get a bee in their bonnet about the lesson they've decided to teach, and overlook the possibility that their students already know the gist of the lesson. If I were you I'd be very tempted to not do it and just make something up. If I were confident enough I'd make up a story that disproved the teacher's point, like "I walked about dressed like an idiot and people were really nice to me."