Our skin heals itself when you get cut.
Unless you have venous insufficiency in your feet and lower legs, in which case you develop ulcers that can persist for years. Human skin is frightfully easy to cut, too, unlike the hide of a cow. A single piece of paper or low humidity can both cause nasty cuts.
We cough when something obstructs our airway so we don't die from it.
That "something" is usually food. Not a very good design at all if the air supply and the food supply are sharing a common passageway.
Poop comes out instead of staying inside of us until we blow up.
Not always, and not particularly well. There are a lot of examples of structural and functional problems in the lower gastrointestinal tract. The long "small" intestine in the human body is prone to life-threatening obstructions, the colon and distal small intestine may be afflicted with Crohn's disease, and then there are hemorrhoids.
Now, if *I* were designing a digestive system I'd make it more efficient so there would be less waste, better extraction of energy from the food, and fewer parts. From the time you take a bite of a sandwich and poop out the end products, that sandwich passes the mouth, palate, throat, esophagus, stomach, small and large intestines (passing through several valves along the way, all of which are prone to malfunction), and the liver, gallbladder and pancreas also have to get involved. What a mess.
Our eyes water when dust gets into it to wash it out.
Our eyes also require a lot of technological assists in order to focus properly, especially as we age. Neurological conditions, cataracts, glaucoma, macular degeneration and diabetes can blind us no matter how much dust we wash out.