They say the Man of Steel can punch dimensions apart. If his fist has a mass of 300 grams and he moves at about 99 percent the speed of light, his punch is equivalent to 45 megatons of TNT. The movement would burn 45 trillion calories, and the energy released would be about 80 trillion Kelvin. 

So what would happen if he punched you? Well, first of all, you literally wouldn't see it coming. Then, he'd knock the atoms out of you, liquifying you at the atomic level. 

Here's the video from Vsauce3 that goes into more detail:

Image: Med PhotoBlog via Flickr CC BY-NC-SA 2.0