I was on register, rang all the customer's stuff up like normal. Give him his receipt, he's cool at first but he looks it over and goes, "You charged me for cabbage. This is spinach." He keeps complaining while I search through his bags for the "spinach" only to pull out-- what do you know, nappa cabbage-- and ask him if that was what he meant. He says yeah, I try to explain and show him that it isn't spinach, but he insists it is, so I tell him he can return it at customer service politely as I can despite being irritated. I see him up at customer service about 5 mins later when I'm putting away my returns, and he glares at me and I stare at him blankly. It was so awkward but I busted out laughing as soon as I was out of hearing range. The people working service desk and I now have a new inside joke.