If a fireman came to work in a police outfit or clown suit, that would be a clear case of nonconformity. Where there's nonconformity, there's difference.
When everyone is acting or dressing exactly the same, there's conformity, not nonconformity. Nonconformity means that someone is doing things differently from the norm. People in authority tend to dislike nonconformity, because it makes people harder to control. Someone who demonstrates nonconformity most of the time is a nonconformist. Too much nonconformity can create chaos, but without a little nonconformity, life would be pretty boring.