Some frankly bonkers opinions in here, not that I should be surprised after years on this board.
Anyone who genuinely thinks Casino Royale or Skyfall are the worst Bond movie are either clinically insane or haven't actually watched all the movies. That isn't to say they are perfect, but does tell me that they probably haven't watched most of the Moore movies for a start.
Some people have said Man With The Golden Gun. The theme song alone makes it impossible for it to be the worst film.
Some people have said OHMSS. Again, no. It has a god tier John Barry soundtrack and it's one of the few films which defined why Bond will never settle down with one woman, albeit that was then done even better in Casino Royale.
It's definitely not Live and Let Die either. That film is rescued by an amazing title song, the unbelievable hotness of a young Jane Seymour and I actually found parts of it genuinely scary as a kid.
And it's not a Dalton film, particularly License To Kill. Dalton suffered from being ahead of his time. Brutal, driven, cold. Reminds me in parts of early Connery, and Craig. A pretty close interpretation to the Bond of the books.
No, it has to be DAD. It has an awful soundtrack, the CG is some of the worst I've seen in a big budget movie, it tries to start with a serious tone (the torture of Bond) but has the invisible car and aforementioned terrible effects to snap you back out. It's just a shit movie. Even the title song is plain rank. Just about the only redeeming feature is just how stupendously hot a young Rosamund Pike is. In my opinion way hotter than Halle Berry.