#3. The Poisonous Spider in Dr. No
James Bond movies are notorious for elaborate murder plots that involve large stockpiles of nuclear weapons, a small amateur army and the equivalent of the gross national product of a small Third World country. So while this one may not be the most elaborate, it is probably the most ill-conceived.
When one bad guy (Professor Dent) meets with Dr. No about their James Bond problem, Dr. No hands Dent a cage with a poisonous tarantula inside and orders that he kill Bond with it. Presumably he means with the spider, though it would have been quicker and more effective to bludgeon Bond to death with the cage.
According to the American Tarantula Society, the only way a tarantula bite could have killed Bond is if he were allergic to it. They are poisonous, sure, but the venom only produces a feeling no worse than a bee sting. So the worst Dr. No would have done to Bond is give him a nasty bruise or a week of muscle cramping in the name of evil.
But even if it had been some kind of genetically modified super-spider, the hard part is trying to get the thing to bite Bond. Ideally you'd need three burly guys to hold Bond down while you cram the spider down his pants. But of course at that point any weapon would work--and work better--than the spider.
Instead they wound up releasing the tarantula in Bond's bungalow where, for all the villains knew, it could have waited for six weeks before accidentally hanging itself in his chest hair.
A Better Way:
Instead of putting a spider in his bungalow, put a dude there. With a gun. To shoot Bond in the face.
#2. The Entire Plot of Smokin' Aces
A mob boss wants a Las Vegas entertainer dead, so he puts a $1 million bounty on his head so that a whole bunch of colorful and apparently grossly incompetent assassins will go after him at once. Also, the assassin is to bring the man's heart to the mob boss, whose own heart is failing.
"For my next trick, I shall make plot continuity disappear!"
A million bullets, knife wounds, shattered windows and one chainsaw to the ass crack later, we learn that the target (Buddy Israel) is actually the mob boss's son. Oh, and that the mob boss is working for the FBI.
Pretty much everyone dies.
Hmmm... it might have something to do with "sending nine hit men to kill one coked up magician in broad daylight, with the understanding that only one of them can collect." Seems to be a lot of room for complication there. Such as, say, the hitmen all killing each other to get the cash.
A Better Way:
The mob boss calls up his son to reconcile their relationship. He shows up at the penthouse looking disheveled and heartbroken. As father and son's eyes meet, they break down in tears and share a warm and loving embrace full of sobbing and apologies for all the wasted years. Then with a heart full of joy and redemption, the father asks for his son's forgiveness. He then shoots him in the face.
#1. The Joker's Bomb Conundrum in The Dark Knight
We would expect a ridiculously long and drawn-out murder plot from a villain like the Joker, a man by whom all clearly deranged and psychopathic murderers are measured. But this one had to have taken the assistance of a room full of supercomputers, and several psychics.
We're guessing the planning went something like this:
"First, we find two empty buildings. Without the cops noticing, we'll secretly sneak in hundreds of drums of explosive liquids, and wire all of them to explode. Next, we'll orchestrate an attack on the convoy transporting Harvey Dent. This will involve blocking busy streets, blowing police helicopters out of the air and launching missiles at the armored car. All of this will be done, not to kill Dent (though that could happen at any moment) but to cause Batman to intervene so that he will throw me in jail.
"So far so good..."
Then, while the whole town is on alert, we go ahead and have our henchmen kidnap both Dent and Rachel Dawes and strap them in with the bombs in the two abandoned buildings. Then I'll send Batman after one of them, knowing that this will result in Rachel being killed and Dent being a certain distance from the explosion as to become grotesquely injured and disillusioned. Then I'll blow up the jail without accidentally killing myself. Gentlemen, it couldn't be simpler."
Really nothing, as long as absolutely every single event happens exactly as it did in the film, down to the millimeter and microsecond.
If the rocket blows up Dent's armored car instead of hitting the Batmobile, if the Batmobile doesn't happen to have a motorcycle hidden inside it, if somebody clears the makeshift roadblock out of the way before the convoy gets there, if traffic allows the cops to get to Rachel before Batman gets to Dent, if a cop happens to be stations out in front of Rachel's building when the cops get the coordinates, if a hunk of debris from the building hits Dent and kills him as he's escaping the explosion...
You get the idea.
A Better Way:
The Joker makes a bullet disappear by shooting Rachel in the face.
To find out how these over the top plans are likely to end, check out 6 Baffling Mistakes Every Movie Criminal Makes. Or check out the baffling plans Hollywood had for some of its greatest flicks in 7 Terrible Early Versions of Great Movies.