A man gets carsick when driving through hills.
So when he leaves his home and hops in the taxi to the airport he tells the driver, "Listen man, I have loads of time to get the the airport. Take the flattest route there, even if it takes longer." And off they go. After a few minutes the driver turns onto a hilly road and the passenger gets sick. "Hey, what gives?? I asked you to take the flattest route!"