Beside its literal meaning, будь здоров is a way of saying "very". That's why we can say
Quote Originally Posted by ReDSanchous
If you mean that someone was severely punished you say:
-Ему досталось?
-Ещё как! Будь здоров!
If a student wants to get to know if their home assignment is big they may say:

-Много нам по английскому задали?-Будь здоров!

No difference if you are talking to a woman or a man (no bud' zdorova), since it's idiomatic.

I don't know why such a phrase may mean very. Maybe it's like "hope one will still be healthy after that"