Stupidity: When the saw yo-yo comes down for the third time, Bond grabs the cord to pull the wielder down off the gallery. That was, when you think about it, a patently bad idea. If the yo-yo hadn't become stuck in the desk, Bond would be collecting his fingers in his hat (note that the blades are still spinning as Bond grabs). (01:15:45)
Stupidity: If Bond and Octopussy hadn't told Kamal Kahn that Bond was in the same room when he went to inform her of Bond's escape, Kamal would not have sent the assassins and had Vijay killed. In fact, Kamal might have just kept searching for Bond elsewhere. It really wasn't a bright decision in the end.
Stupidity: Khan's backgammon games make no sense by conventional rules. He claims to have won the first game even though he has a counter on the bar. His opponent is well behind but since he hasn't borne off any pieces he should have continued to avoid losing a gammon and having to pay double stakes. In the second game Khan rolls a double six but he doesn't bear off before Bond takes his turn. (00:29:30)
Chosen answer: The satisfaction of knowing he'll win, the thrill of pulling one over on someone; maybe like Goldfinger, he just doesn't like to lose under any circumstances.
Captain Defenestrator