I usually try to give my pax the benefit of the doubt. We don't know what kind of a day they may have had before crossing our threshold. Not that it excuses out right rude behavior, it does make it a bit easier to tolerate. Killing them with kindness works for me. By this, I don't mean rewarding bad behavior but just not allowing their poor manners affect my good manners!
That said, some folks are just jerks.
Just don't let them get you down!
There can be culture differences that come into play as well. I hate it when some goof snaps their fingers to get my attention.
Dea