If you're the type of person who enjoys picking apart movies, by far the easiest (and most amusing) starting point is to simply rewatch the movie from the villain's perspective. What does the villain actually want? Does the way he's going about it make sense at all? The answers are usually ridiculous.
That's because most movies aren't written that way; the bad guy is just there to create conflict and cool scenes for the hero, regardless of whether there is any logic to it from his own point of view. We've already gone over some villains who accidentally saved the day with their own actions. But at least those bad guys screwed up without realizing it. Here are the ones who seem to go out of their way to sabotage their own plans ...
5 Spider-Man 2 -- Doctor Octopus Needs Peter Parker Alive, Throws a Car at Him (For No Reason)
When an accident turns Professor Otto Octavius into a supervillain (as if he wasn't always destined for that career with a name like that), he starts dressing like a subway pervert and adopts the identity of Doctor Octopus, but still intends to continue his experiments in nuclear fusion ... only in an EVIL way. Doc Ock needs some tritium to finish his reactor, so he makes a deal with Harry "Green Goblin Jr." Osborn, who will give him as much tritium as he wants if Ock brings Spider-Man to him.
"I'm in a position to negotiate, apparently."
Problem is, Spidey has been sort of MIA lately. Since it's common knowledge that the only one who can get a hold of him is Peter Parker, Doc Ock needs Peter to lure Spider-Man into a trap, which he forces him to do by kidnapping Peter's love interest, Mary Jane Watson. Very simple.
How He Tried to Screw It Up:
Doc Ock needs both Peter and Mary Jane to be alive for his plan to work ... and yet, when he finds them sitting in a cafe, literally the first thing he does is launch a friggin' car directly at them.
"Hey, Peter! PETER! Over here!"
There's no way two normal people would have survived that -- the only reason Peter was able to duck out of the way is because of his spider-sense and Neo-like reflexes, which Doc Ock obviously doesn't know he has. Otherwise, both he and Mary Jane would have been squashed by a flying vehicle, rendering Doc Ock's entire plan pointless. No Peter, no one to find Spider-Man, no tritium.
Was the whole point of the car-throwing stunt to get Peter and Mary Jane's attention (by decapitating them)? Or was that just his way to say "hi"? Maybe Doc Ock was trying to open the window and there were no trash cans around. Of course, the more likely explanation is that they just needed an excuse to shoot a scene with Peter ducking out of the way of a flying vehicle so they could put that in the teaser trailer.
If you look closely, you can see the dollar signs reflecting off Sam Raimi's eyes.
Also, killing Harry's two friends would have only pissed him off (he specifically says, "Don't hurt Peter"), and then he'd never give the tritium to Ock. Why the guy with the huge metal arms didn't just take the tritium in the first place, we'll never know.