Do men usually use ぼく when writing a diary? Is it appropriate to use わたし?
ぼく is spoken, commonly used by men, わたし (privately) is more formal, mostly used in written language and social language, and ゎた (privately), but less used. There is also a "ぉれ" in spoken English, which is also very commonly used, but I don't remember whether it is used by men or women.