I find myself developing unhealthy habits as a passenger.
Clutching my purse in my lap to keep me from grabbing the steering wheel.
Holding the "OH CRAP" handle that is above my door. (this works well on corners)
Pushing my foot so hard on my imaginary brake that I think I sprained my ankle.
Giving instructions in a ridiculously calm voice. Like the one you use when you are trying to convince someone not to jump.
I have also seemed to develop a severe lean to the left. I only noticed this though when we are driving by cars that are parked on the right side of the road. This lean almost always is accompanied by a cringe and purse clutch. I like to call this the "trifecta of not looking panicked."