Here's my Dollar Tree story, only it's the local supermarket this morning:
After waiting in line for about 10 minutes, I finally got my items on the conveyor belt. I finally get to the head of the line. As the customer in front of me gets their receipt, the register paper runs out. So the clerk puts in a new roll of paper, which crashes the register. "We're closing the lane, folks!" So I gather up my items, putting them back into the cart, but by this time all the people behind me in the line have scattered and joined other open lines, so I am back at the end of another line and have to wait ANOTHER 10 minutes to check out.
I know, first-world problem. But it was still annoying.