Wint and Kidd killing Shady Tree with a "Bang!" Flag Gun that fires real bullets.
Plenty O'Toole having dinner with Bond, ending with Plenty inviting herself to Bond's apartment. Then, after the "pervert's convention" throws her out the window, Plenty returns to Bond's apartment soaking wet and wearing nothing but a white Modesty Towel to hide her shame in the hopes of retrieving her clothes and to see what has become of Bond. After seeing him having sex with Tiffany an angry Plenty almost leaves... but not before going through Tiffany's purse and finding her address, explaining how Wint and Kidd confused her with Tiffany.
Executive Meddling: When the film aired on ABC the network had the scene where Lana Wood, as Plenty O'Toole, walked around wearing nothing but a flimsy pair of see through pink panties artificially altered to make it appear as though she were wearing a black bra with black panties - despite the fact that her backless purple satin dress clearly showed that she had no bra.
Fatal Method Acting: Closely averted by Lana Wood when the cement block she was tied to in the swimming pool slipped down the sloping floor of the pool and dragged her underneath. Fortunately crew members spotted and rescued her.
Hostility on the Set: Relationships between Sean Connery and the EON producers (Albert R. "Cubby" Broccoli and Harry Saltzman) were acrimonious at best since at least You Only Live Twice (he felt underpaid among other things, which is why he left the series after that film). Connery was brought back with a huge paycheck after the exit of George Lazenby, and proved difficult to work with on the set of Diamonds are Forever. He outright refused to act whenever Saltzman was on the set.
Looping Lines: Lana Wood's lines were looped in post-production for some reason.
Money, Dear Boy: Sean Connery received $1,250,000 to come back for the role, but used it to set up a charity to help poorer families in Scotland with their education costs.
Old Shame: Defied, at least as far as Jill St. John is concerned. In the Bond Girls Are Forever TV special, she has a few fairly scornful things to say about actresses who view their Bond Girl roles this way.
The Other Darrin: Blofeld (which makes him get hair this time) and Leiter (the fourth actor to portray him).
Recycled Script: In a lot of ways, the book is a remake of Live and Let Die - Bond goes to America, battles a gang that specializes in smuggling some precious mineral, and entices a High-Heel–Face Turn from its sole female member, a woman who had previously sworn off men.
Scully Box: Lana Wood needed one when on screen with Sean Connery. Except of course, in the scenes where she was lacking her clothes, for which she was given extra high heels to wear in order to compensate for the height difference, as a body double would not have worked for obvious reasons.
Technology Marches On: The codes that control the satellite are stored on a tape cassette that protrudes prominently in Tiffany's bikini bottom. Today, a flash drive would've been more discreet, though there'd still be the communication SNAFU between Bond and Tiffany
Adam West was offered the part of James Bond for this film. He declined out of respect, saying he felt the role should only be played by a British actor. Burt Reynolds and Clint Eastwood also declined Bond for the same reason.
In Richard Maibaum's original screenplay, the villain was not Blofeld, but Auric Goldfinger's vengeful twin brother, to also be played by Gert Fröbe. This was scrapped when Tom Mankiewicz was brought in for rewrites.
Richard Maibaum's original idea for the ending was a giant boat chase across Lake Mead with Blofeld being pursued by Bond and all the Las Vegas casino owners who would be sailing in their private yachts. Bond would rouse the allies into action with a spoof of Lord Nelson's famous cry, "Las Vegas expects every man to do his duty." Maibaum was misinformed; there were no Roman galleys or Chinese junks in Las Vegas, and the idea was too expensive to replicate, so it was dropped.
Maibaum may have thought the eventual oil rig finale a poor substitute, but it was originally intended to be much more spectacular. Armed frogmen would jump from the helicopters into the sea and attach limpet mines to the rig's legs (this explains why frogmen appear on the movie's poster). Blofeld would have escaped in his minisub and Bond would have pursued him hanging from a weather balloon. The chase would have then continued across a salt mine with the two mortal enemies scrambling over the pure white hills of salt before Blofeld would fall to his death in a salt granulator. Permission was not granted by the owners of the salt mine. It also made the sequence too long.
It was originally revealed that Blofeld survived the end of the film and the filmmakers were planning on bringing him back for one last outing in the next film, but the legal controversy made that impossible.
Irma Bunt was supposed to reappear in this film and presumably, Bond would extract revenge on her for Tracy's death, but Ilse Steppat died just days On Her Majesty's Secret Service was released.
Mr. Wint originally killed Dr. Tynan by shoving the scorpion into his mouth.
Paul Williams was originally cast as Mr. Wint. When he couldn't agree with the producers on compensation, Bruce Glover replaced him.
Charles Gray (Blofeld) earlier played a British agent in You Only Live Twice. Ironically, said agent is murdered by SPECTRE, so he is basically playing the man ultimately responsible for his own death.
David Bauer (Morton Slumber) had previously played an American diplomat in You Only Live Twice and Shane Rimmer (Tom) played a Hawaii Radar Operator in the same film (and would go on to play a bigger role as the American sub captain in The Spy Who Loved Me).