Someone must think you can handle it. Just smile and nod at the crazies, and always answer "aisle 4" to whatever they ask, just to make the time pass quicker.

Back when I was a checker I always hated being the 4th person to come in.  The first person went into lane 5, a full service lane.  The next person went into lane 4, express lane cash, check or charge.  The third person went into lane 6, another big lane.  The fourth person was put in lane 1, which was 1-10 items cash only.  I swear on most days I felt like grabbing one of those dividers people use to separate their orders and whacking a few people on the head with it.  I got tired of people's impatience.  I was actually a fast checker but we get a lot of old people who take forever to dig their money out.  The customers waiting in line acted like it my fault.