Where Stupid Collides

I was with my wed morning group today and we were cutting up as usual. One is relaying the story of going to a local fast food joint to pick up some lunch. He is second in line behind a lady who is ordering for three separate "to go" orders. The girl behind the counter gets one of the orders wrong (murphys law) and has to get a manager and all that jazz.
now, more than likely you have been in this situation somewhere. Mine usually occurs at Wal-Mart. I'll scan quickly for the shortest line and get myself in it. Unfortunately, the reason the line was short is because other exasperated customers have decided to find another due to the incompetency of the cashier and/or the customer in line. I'll look up and the little "i need assistance please" light is flashing. Now this only occurs in direct correlation to the amount of time I have remaining prior to another obligation. The less time the more frequent the occurence.
Which leaves me with this: If you put two certain variables together, the outcome will not be desirable. Hence, Stupid people should not work where stupid people order. Its a recipe for disaster I'm telling you. I'm not sure their shouldn't be IQ meters at least on one end of the deal. Either the worker or the shopper. Would make things go a lot smoother.