Why are customers so stupid?

I work in the grocery department in a store and people don't bother saying excuse me before asking.They just blurt it out, and some of them do it standing 2 miles away looking the other way. At other times, when I am talking to another employee, a customer will just interrupt to ask someting, once again without bothering to say excuse me first. why don't these sons and daughters of bi*ches say excuse me, these ba*tards and who*res.