Cashier lines work the checkout: scanning, discounts, and being rung up one item at a time. The captive thirty seconds at the till is both the joke's setting and its constraint — whatever you open with has to land before the receipt prints.
Respect the register: staff at work deserve lightness, not a hostage situation. The best use is between colleagues or once the name badge is off the clock.
The checkout has a strict comedy format: thirty seconds, an audience queueing behind, and one shot at a smile before the receipt prints. Material that respects those limits — one light line, no encore — reads as charm; anything longer reads as holding up the queue.
The real romance arc is the regular's: same till, accumulating banter, until the name badge has a name you actually use. Off the clock, all limits lift. The service-counter siblings live with the barista lines, and the full rota is in the occupation collection.