"Peter is not a bad man."
Translation:Péter nem egy rossz ember.
Here, in this context, "ember" is like "person". So, you would use the same "ember" for both men and women.
If you say "nem egy rossz férfi", or "nem egy rossz nő", you are talking about the person's attractiveness. Like, "look at that woman, not baaad, not bad at all!" - could be "nem (egy) rossz nő!" As in "a very attractive woman". Or "nem egy rossz férfi" is a "handsome man". The same goes with a positive sentence. She is a "good woman" - "jó nő" means a very attractive woman.
So, choose your words carefully. :)
For this sentence to be clear to the English speaker, it should read that "Peter is a good person." Using "man" in English has a very specific connotation, and does not get used generally. You would never say in English (Except maybe to be ironic) "Judy is a good man." The intended connotation in Hungarian should use the term "person" for the English half of the translation.
The sentence is: Peter is not a bad man. We don't know if the person who wrote it meant physically (in a colloquial way) or not. Using ferfi should be accepted, as it is grammatically correct. To avoid any confusion the sentence should be: Peter is not a bad person. Your comment is nevertheless very useful and I will rebember it
Well, personally I have never heard "... not a bad man" applied to anyone's physical appearance. But it may be, I don't know. But in Hungarian, that is very likely what is meant. So, if you want to be literal, be my guest. If you want to convey the same meaning, I recommend you stick to "ember". :) Or use another adjective. But the general statement for somebody's good-naturedness is
"Nagyon jó ember" - "A very good person"
Man or woman.