This tutorial will show you how to use your iPod to mark songs for automatic deletion so you won't have to remember to do it later. It's the next best thing to having a "delete" button on your iPod. And don't worry this won't delete songs from iTunes, just from your iPod. Now when you hear a song on your iPod you don't like anymore, you won't have to remember to delete it when you get back to your computer. This method also comes with some other nifty benefits, I'll describe later on.
http://www.instructables.com/id/Automatically-remove-unwanted-songs-from-your-iPod/