What are people thoughts about tipping drivers of airport shuttles? I am talking about rental car, hotel, and inter-terminal shuttles, not shared vans and the like.

Maybe this is a personal hang-up, but I hate having people grab my luggage. I just feel more comfortable if I handle it myself. But most of these shuttle service drivers are like mad men trying to lift the luggage onto the rack and then take it off. I think LAX is the worst about this. Some kind of golden touch "I touched your luggage now you owe me a tip". I have gotten to the point now if they do that I simply don't tip them, and let them get grumpy. I hate that entitlement attitude.