His name is Reinhard Kuester, and he's smiling from within his very own homemade sub. It's named "Nemo", and it can dive to 98 feet. It's seen here making its maiden voyage in the Helene-See lake near Frankfurt, Germany.
People make their own planes, I know, and cars and houses. Any of those seem lke a better choice. I'm not sure why you'd make your own sub. You don't need to defend your shores, you don't need to deploy nuclear weapons. You can't really go all that fast. All you can do is go down and look at things - unless you spend a lot more time and build some sort of mechanical arm.
You could die. You'll probably get cold and wet! And if the guy in front farts, forget about it! (Surface!
Surface!!)