not know enough to come in out of the rain
To not have very much intelligence or common sense, especially when facing or presented with a difficult situation. I'm not surprised his latest business venture failed too—that fool doesn't know enough to come in out of the rain. Cut him some slack, Jim. You didn't know enough to come in out of the rain when you were his age, either.
not know enough to come in out of the rain
Fig. to be very stupid. Bob is so stupid he doesn't know enough to come in out of the rain. You can't expect very much from somebody who doesn't know enough to come in out of the rain.