In Thelma's motel room, buck-shirtless, J. D. brandishes a hairdryer as a gun. A hairdryer is a household item generally associated with women and domestication, but here it's given the attributes of an item associated with violence and masculinity. 

You see where this is going: the hairdryer suddenly becoming powerful and dangerous is a symbol or the way Thelma and Louise have gone from domesticated to dangerous themselves.