When I was living in Aichi, a Taiwanese-Canadian friend related an account to me. She said that when she was at a Japanese friend’s place, she threw a friendly jibe at the friend to get her to shut up by saying うるさい (urusai, which literally means “noisy”). That friend’s mother overheard it and came to my friend and said, “You shouldn’t say urusai, you should say やかましい (yakamashii),” which means the exact same thing, except in dialect. At that time, I just thought may be it’s less harsh to say yakamashii instead, so I made it a point to avoid using urusai which served me well during my time in Aichi.
After I moved to Tokyo, I met a girl from Chiba with whom I went out for a few times and it just so happened once, she teased me about something that I responded with “yakamashii” and she was a little taken aback. She asked me, “Did you just say yakamashii?” and I replied, “Yea.” She then told me, if you say that in East Japan, people are usually taken aback. It’s less harsh to say “urusai.” It’s the same with バカ (baka) and アホ (aho), both of which means “stupid,” with the former being the standard Japanese and the latter being the dialect. In East Japan, it’s less harsh to use baka and the exact opposite in West Japan.
As a former linguistics student, my instinct to analyse things switched on and I realised that in West Japan, where dialect is the more oft used language, using the dialect form of “shut up” and “stupid” (i.e. “yakamashii” and “aho”) is more natural and it establishes a form of solidarity with the people, so they recognise it’s a friendly jibe. If you suddenly switch to the standard Japanese of “urusai” and “baka,” it creates the image that you are distancing yourself with the people and are being serious about scolding them in using standard Japanese. On the other hand, in East Japan where standard Japanese is the norm, dialect, being seen as a reduced form of the standard language sounds relatively harsher and more crude.
Now even scolding people is an art.