I got yelled at once for being in the "10 items or less" express lane. I had like 15 items and, like Clodfobble, got called over from another line by the clerk. "I'll help you over here, sir".
I'm unloading my stuff onto the conveyor when this snotty bitch comes up behind me and says "that doesn't look like 10 items or less". She caught me in a foul mood after a shitty day at work and not wanting to stop at the store, but the wife insisted. You should have seen her face when I quietly asked her "what are you...you fucking grocery police?". I only said it loud enough her for her and the clerk (who was trying not to laugh hysterically) to hear. My day got a whole lot better after that.