The Idiot's Line

The line which you always seem to get onto at the supermarket checkout, the highway tollbooth line or in the bank.

The former always has someone who has a limited supply of cash and no credit card so they have to withdraw some items from their cart and wait for the checkout girl to recalculate and say "you're still 9.69 dollars over".
Or in the second, someone who drops his change and has to stop and scramble under his car.
Or in the latter, you are behind someone who suddenly pulls out wads of cash from his under his shirt for depositing in different accounts.