....and what do you mean by that? I certainly hope that you aren't thinking about stabbing yourself with a LiveUSB...
[from my experience,] If you're new to this (which it seems that you aren't, but I'll go with it) you probably want to go with Ubuntu or one of its friends (Xubuntu, Lubuntu, Kbuntu...). That's where I started. Just poke around in there, screw up your configuration files, reinstall, and repeat, and each time try to change as much as possible without breaking the OS
. Seriously, though, you want to get used to the terminal. The CLI is your friend.
If you're at the "new-ish" end of the "intermediate" area (where I think I'm at now) setup some server distro (I went with Ubuntu Server, since it's based off the Ubuntu & Friends that I played with as a newbie) and see what you can get to work. This time, try not
to break anything, but instead setup whatever you feel like.
If you're towards the "expert" end, go for something like Slackware. I tried messing with it, but didn't have the time to figure it out. If you have the time, patience, and Internet bandwidth (for the forums, of course) it should turn out to be a great project.
Good luck, and have fun!