Or even better, ask them to book a rental car when they ask you for a ride from the airport. And lie to them that you are not in town. If you do this for a couple of times, they will get the message. On a different note, this reminds me of a couple who used to live next door. They used to request (which sounded more like an order) my DH to drop them off at the airport and pick them up when they return. And can you believe they asked us this, when they booked tickets from an airprt which is atleast 250 miles from our place! So, there are many shameless people in the world who do not hesitate before asking favors!