I don't have my phone close right now but on the phone while in the slacker app if you hit the BlackBerry button there is something I belived called reset. It will clear your favorites. It tells you what it will do before you click okay. I'll post clearer instructons when I'm with my phone.
does anyone know how to un-favorite a song on your blackberry?
I have my phone now. Go into Slacker app. Hit your BlackBerry menu button and you will see "Reset messages" this will clear all your favorites. I'm not sure about clearing one song from favorites.
I just thought of something else. You go to edit station and from there ban or unban a song and I think you can unfavorite a song. Try from your Berry but you may have to do it from PC.