why is that? Is it possible to delete your DB?
how to make your gamedatabase private?

No you can't delete the games or DB either. Once a game is played on the site it belongs to both players and the site.

You have to be inured to embarrassment. Our bad moves are out there for all the world to see, doesn't bother me. One thing you could try is two different accounts with different IP addresses, one for your normal days and the other for the times you're all bright-eyed and bushy-tailed and ready to take on the world. Two or three days out of the year I can play like a master, but I haven't had one of those days since I joined the site.
You can't.