"I once had a guy place his order, and then say 'And give me one of those spaghetti appetizers.'
I had been working there for a couple months, and we had no pasta dishes whatsoever on the menu. I politely tried to clarify this, but he wasn't having it. He just kept getting more irate. He insisted that he eats here all the time, and he always gets the spaghetti appetizer.
Eventually, he gets up from his table, storms over to another one, and points at what he wants on another diner's table. He was pointing at their cole slaw. And yes, as far as he was concerned, I was still the asshole for not knowing what he was talking about.
Edit 1: Our slaw was a southern style slaw, where the cabbage is shredded. So, the cabbage is in strings, but you would still have to be some sort of weirdo to confuse it with noodles. And a few people have mentioned a Dane Cook bit. I'm not familiar with that joke, but after doing some googlin', it appears that is a joke about messing with staff at a restaurant. This happened in 1994, and the customer was an older, well dressed guy out to dinner with his wife. I'm positive he wasn't f***ing with me, he was just an obnoxious a-hole that expected me to know what his confused mind was talking about."