I don't want you to think I'm making this up to have fun at your expense, because what I'm about to lay down on you is totally true.
It all started when I was a small child and my father had the problem. He went in for surgery (which I'll describe to you later :D ) Dad was a man who enjoyed being barefoot, or maybe wearing flipflops if he had to. Shoes as such were strictly a work and golf kind of item. When Dad came backfrom the podiatrist one toenail was gone, the other was just left a sliver of nail. It looked kind of like a piece of onion. It turned out that his father had had toenail trouble too, but prefvented it from getting out of control by cutting V-shaped notches in his nails.
My brother had what might be one of the grosser ones. He was playing JV football when the problem began to manifest itself. The toenail would cut the toe from the inside and his socks would be bloody and crusty when mom got around to laundering them. Once I saw him rub his toe and a bunch of pus came out. Not long after that mom had him get his toes operated on. The operation was not as severe as my father's and now my brother has pretty reasonable looking toes.
My case was a bit more like my father's. A bit after my brother got his, I noticed some pain on the edges of my toes. Not wanting to let them get infected like my brother's had been, mom made me get them taken care of right away. I will now describe the operation. They put novocaine in, told me to read a magazine, and chopped away. Of course I had to look down, at which point I was less than pleased. The worst part was when they disinfected the wound left from ripping out some of the toenail root by putting some silver compound on a stick and jamming it into the would. That's when I stopped reading the reader's digest and started biting on it. They say 98% of people never need the operation again. I was a 2%. Now the nails look like dad's did.
When there is only a partial nail left, things like this happen more easily:
http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=105x6799883#6799984