He doesn't know enough to come in out of the rain...

From a dictionary of Idioms:

Not smart 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.

 

This picture was taken at a campaign stop yesterday in Glen Allen.

He is obviously too stupid and doesn't know enough to come in out of the rain.

The Prosecution rests its case.....The man is an idiot.