Mayo is fucking gross. Any condiment/sauce made with mayo fucking sucks and ruins food. It's used by default in too many foods in the US. Often without even announcing it, and then you have to send it back.
American cheese is crap, especially white American cheese. Yellow American cheese is okay on a burger, but basically any other cheese would be better. And when it comes to eating on its own or with crackers, there's no comparison.
Black pepper is overused and other spices are underused. Salt is a flavor enhancer, whereas pepper just overwhelms. It should be used sparingly. Instead, a lot of people just douse it on everything and it ruins a lot of food.
Sweet barbecue sauce sucks. Mustard based BBQ sauces aren't much better. Tangy tomato based sauces for the win. Alabama white sauce is an abomination.
A lot of spicy food sucks. It's used as a cover for a lack of flavor. I remember a Jamaican guy I knew talking about how a local Jamaican/Caribbean place sucked and they just over-spiced the food and people thought it was good because of that, but it was crap. It's about flavor, not heat. You can have both, but flavor first.