The Jesus Fish Phenomenon

Why is it that every car that has the Jesus Fish on the back has to drive like a 90 year old woman? It doesn't matter who is in the car driving, the power of Jesus compels them to go 10mph under the speed limit. God is on your side, right? Don't worry about driving fast and reckless. Or, just get out of my way. Someone should do a study on this. The affects of the Jesus Fish on annoying driving. Get on that, science!