Going out to eat can be fraught with stress, because there's always that nagging feeling you're doing something wrong and the whole restaurant is staring at you. And with good reason: you ARE doing things wrong, and they ARE staring at you. So stop making these cringe-worthy food faux pas and rest easy in the knowledge that you are only drawing stares for your comical physical appearance.
Don't put ketchup on a hot dog in Chicago: Really, this should go for any hot dog, anywhere. Ketchup belongs on French fries. But especially don't ask for ketchup in the hot dog capital of the world. Some places will straight-up refuse you; others will simply mock your ignorance. This doesn't mean you need do get the full-on salad that is a traditional Chicago dog. Get just mustard and relish. Get chili. Wrap it in bacon. But no ketchup. Ever.
Don't use a knife and fork on pizza: There's an exception here for deep-dish, but, generally speaking, silverware is to be avoided on your garden-variety, highly foldable pizza slice, unless you're three years old and Mommy is cutting it into small bites for you. And, even then, it's borderline. And what are you doing reading this site, three-year-old? WHERE ARE YOUR PARENTS?!
Don't do any of the things you do at a sushi place: As with steak, the magnitude of the transgression increases with the quality of the sushi establishment. Don't rub chopsticks together to get rid of "splinters" -- it implies you think they use subpar chopsticks, and do you honestly know anyone who has ever gotten a mouth splinter eating sushi? Don't dump the wasabi in the soy sauce and mix it together (particularly if the place grates its wasabi fresh). Don't dump a bunch of soy sauce on a maki roll that the chef has already accompanied with an array of sauces and accoutrements. It's a wonder you aren't forcibly removed from sushi restaurants on a regular basis.