What do you mean old people are not good?

Bad old man means an old man with a bad heart

"You bad old man is very bad", because there is a "you" at the beginning, which is the second person's address, so you should say it to your face. Whenever a woman says this to your face, it should mean flirting. Maybe this "bad old man" molested this woman, or maybe he had other physical actions to provoke her. Anyway, he didn't really scold you, and he didn't really say you were bad.

Many things women say are against their will, even against their will. Maybe she said "you are a bad old man", but in fact she still likes everything you say and do. Being able to say this in person, at least for her, is not how much she resists you, but perhaps encourages you to go further.

If a woman says this old man is bad on other occasions, it should mean that she really thinks this old man is bad in some ways, and it is also reminding other women to be careful of this man and beware of him.

So, whatever it is, it depends on the occasion. Different occasions mean different things.

Being able to say "you are a bad old man" to his face is actually rich in connotation. If you add that the woman was laughing, or that she was shy, you should take bold action.