I cant remember just ONE bad OP but I can honestly say Many OP's were fuckered thanks to Ameridubs, such as DBZ (100% electric guitar, and screaming "dragon dragon dragon ball z" is bleh...) and One piece are the first that come to mind...
I prefer Original Jap OP...
EDIT:
Soooo much better...
Ahh the NOSTALGIA!!! (I spent about 10 mins trying to remember that word damnit...)
Dragonball theme songs really brings back many memories :DD
For me, I practically grew up listening to these korean versions of original dragonball and dbz
Spoiler:
Anyways, back to the topic, my least favorite opening, aside from previously mentioned GSD's Wings of Words, was:
Spoiler:
Code Geass R1 Second Opening, Kaidoku Funou by Jinn... I just can't help myself hating it. I think that the song did not fit the mood of the second half of CG R1, and the vocal's voice was... not for me.
Gasaraki op. Just some random monochrome image with Japanese writing. A really boring OP. No point of me posting the vid, you'll just waste 1:28 minutes of your life watching it...