1. Well-done steak. They use less-desirable cuts of meat, because it's harder to notice when they're well-done. If you have a specific reason, tell your waiter so they know why you’re asking for it. For example, pregnant women should go with well or medium-well.
2. Mussels. One bad mussel can make you really, really sick. So it's risky. Anthony Bourdain once said he'd only order them if he knew the chef personally.
3. A really expensive cheeseburger. The markup is ridiculous, and it's rarely worth it. They MIGHT be using expensive ingredients to justify the price tag. But burgers are supposed to be made with cheaper cuts of meat anyway. So it's just a waste of money.
4. The seafood special. It's usually made with seafood that's about to go bad. So it's really just a way to clean out their fridge.