A friend showed me the following video a few minutes ago. He says that it's real, but I can't believe that actually. What do you think?
The video show some guy hammering a nail into his nose.
Howstuffworks has a pretty good explanation of this:
As you can see in this image, there's plenty of space, but there might be some need to "wiggle" the spike in and then push up the nostrils a bit.
It is quite likely true. It is a common circus/freak-show stunt.
The skill is called the Human Blockhead. ("Skill", not "trick", because the nail is real and does go into the head.)
Here's a video of another guy inserting a 4-inch nail into his nose in a similar way.
It involves inserting the nail into the nasal cavity, and relies of people not understanding the anatomy of the skull for its impressiveness. This How Stuff Works article goes in detail about where to stick the nail.