I'm going to split this into two categories:
Original soundtracks and "dubbed" soundtracks.
The worst original soundtrack I've heard is Inuyasha. If you watch it, you'll know that 90% of the BGM is silly wacky chilling music. Very bad sounding too. twitch :mellow:
I think there's one that I can actually REMEMBER. It's not good.
For dubbed, FUNi's DBGT takes the cake. The dubbed soundtrack is GOD AWEFUL. There are like THREE pieces of BGM, played over and over again. WHY?! WHY GOD WHY!!! runs off