If you're ever standing on a mountaintop when a dark cloud passes overhead and your hair stands up, get off the mountain fast. how would your hair have acquired the charge to make it stand up?

The hairs would have acquired charge by the passing of dry winds resulting in the loss of electron.

Explanation:

While standing on the top of a mountain if a person gets its hairs stand up after a cloud passes over, this might happen due to the static electric charges on the lower surface of the cloud  are opposite in nature to that of hairs which the hairs would have acquired by the passing of dry winds which would have resulted in the loss of electron from the hair tip.

Similar case happens when we rub a dry plastic ruler or a dry plastic comb on our hairs.

the body's situation won't change the forces are equal opposit and on the same body