Whenever I learn about the way some weird function of the body works, I can't help but marvel at how 'smart' that mechanism is. Fainting is a good example. When the body gets a lot of sensory data that says it's in trouble, it knocks your legs out from under you to help blood rush to the head so that your brain won't die. I mean, that's insanely clever if you think about it, and while it's often uncomfortable and sometimes a nuisance to people to black out (while giving blood for example,) that whole mechanism is just the body's way of taking care of itself. It's as if the body knows that if you black out, you can't stand, and if you can't stand, you can't pull blood away from the brain that needs to be going there. Damn smart, if you ask me.
But for every curiously well-designed function like that, there's an equally dumb design idea somewhere. Take a rash, sore, skin lesion, or alergic reaction, for example. When you have some part of the body that itches, where the skin seems to be demanding attention, it's almost always the exact wrong thing to do to scratch the itch. Scratching spreads whatever it is that's causing the problem and makes everything worse. In a way, the itching sensation is probably good because it alerts you to the fact that something's not quite right, but the fact that scratching an itch yields such a satisfactory result seems counterproductive to the goal of fixing whatever is wrong. If this were smartly designed, things would feel much, much worse when you scratch them to keep you from doing it.
Lots of other stuff works this way: poison tastes bitter so that we will avoid it, or rather, we are programmed not to like the taste of poison which happens to be bitter. The biological mechanics of sexual attraction are astounding and somehow work terrifically well in a species that has held on to a lot of natural fragility by enhancing life with technology. But there are times when the processes that go on behind the scenes just don't seem to help or make much sense if you imagine the body as this machine designed for a singular purpose: survival.
Now none of that has anything to do with 'who' might have designed the body, or if a designer is indeed required, or what the implications are if the body is or isn't a perfect machine on it's own--that's a topic unto itself. I just found the idea of scratching an itch to be something that runs very counter to the way it ought to work.