When is it rude to call someone by their given name? [duplicate]

Question

Would it be considered rude to suddenly start calling someone by their given name, like, should you ask permission to do so first? if you don't ask permission, and this someone only wishes to be called by their family name, is it seen as though you're mocking them, or intentionally being rude?

edit: i mean, how rude would it be seen as? is it seen as taboo, or just generally greatly frowned upon in society?

edit: I have looked at the posts addressing politeness, but it doesn't answer my question here.

Answer 1

For example, his name is Taro Okamoto. Taro is his first name and Okamoto is his family name.

In formal settings, for example, you're on business, in a company, or in a class at school, you should call him "Okamoto-san."

"Okamoto", "Taro", "Taro-san", "Taro-chan", "Taro-kun" are not appropriate. "Okamoto" and "Taro" are even rude and offensive. No matter how close you and Mr.Okamoto's relationship is, you should call him "Okamoto-san" in a formal setting. It is a matter of Japanese grammar, the Keigo-system. It's more like in English you should call him "Mr. Okamoto" in a formal setting.

In informal settings, for example, in a private party, or in a conversation between friends, you can call him:

(The higher the number, the closer your relationship would be.)

1. Okamoto-san
2. Okamoto-kun
3. Taro-san
4. Taro-kun
5. Okamocchan or Okamocchi
6. Tarocchi or Tarochan
7. Okamoto
8. Taro

First, you should start calling him "Okamoto-san" and I think it's safer to ask him the permission about what number you may call him.

Hope this helps!

Answer 2

Would it be considered rude to suddenly start calling someone by their given name, like, should you ask permission to do so first?

Yes. If the someone's name is Barack Obama, it's natural to call him Obama-san.

if you don't ask permission, and this someone only wishes to be called by their family name, is it seen as though you're mocking them, or intentionally being rude?

Before answering this question I have to say that there seems no custom in Japan to propose others how you prefer to be called.

Anyway, it's a very difficult question, because Mr. Obama would very soon understand that you're not a Japanese judging from your appearance and/or the ability to use Japanese.

If you are a Japanese, what is asked by the question is very rude. But, in the situation you are understood as a people from other country, Mr. Obama would try not to make you annoyed and also he would try to understand your behaviors including how you call his name. So, even if you call him Barak abruptly, he is sure to understand that it is the natural way to call one's name in your culture without thinking you are rude.

If you would like to have a nice time with Mr. Obama, I recommend you that you call him Mr. Obama and you would propose how you prefer to be called by Mr. Obama at the meeting. If you propose Mr. Obama that you want to be called with your given name, he might possiblly propose that he also prefer to be called simply Barak only in the meeting.