People put the strangest things into their dishwashers. I once had a tenant who ruined an expensive pair of hiking boots by washing them in his dishwasher. Here is a list of things that you should never put in your dishwasher.
Wooden items. The water and heat inside a dishwasher can warp and crack wooden items, like salad bowls, cutting boards, and utensils with wood handles, like steak knives.
Cast iron cookware. Seasoning prevents cast iron cookware from rusting, but a dishwasher will remove it.
Non-stick cookware. Most non-stick coatings do not hold up well in the dishwasher.
Aluminum cookware. Aluminum pots and pans can oxidize in a dishwasher and turn dull or even black.
Insulated mugs. The heat of a dishwasher can damage the vacuum seal between the inner and out walls. Once that happens, the mug will lose its ability to retain heat.
Sharp knives. They will lose their edge.
Dishes with big pieces of food on them. You don’t have to rinse dishes before loading them in your dishwasher, but you should scrape food off of them first.
Crocs. It might seem that the easiest way to clean Crocs and other rubbery footwear is to put them in the dishwasher, but the heat in a dishwasher can shrink and warp them.
Computer keyboards. Yes, people have done this. I know how hard it is to clean a computer keyboard and get the dust and dirt off the sides of the keys, but you will ruin your keyboard if you put it in a dishwasher.