I would argue that such weapons already exist in the D&D rukes.
Examples:
Spiked Chain. It has metal protrusions coming out of each link. So that the user would puncture his own hand. That is dumb. Banned in any game I GM.
Mercurial Weapons. A hollow tube filled with a lethal metal. Only someone that has NEVER actually used a sword would think of this... or someone that has no knowledge of how dangerous mercury is... Banned in any game I GM.
Dire Flail. Best way in the game to smack yourself in the back of the head. Banned in any game I GM.
Any weapon based on something seen in a computer game, especially something from Final Fantasy.
Double Sword as depicted in the games illustrations. You need a fairly high ratio of grip to blade to use such a weapon. It's more like a short staff with sword blades on the end.
All of these weapons can only exists within a fantasy game. You don't seem them in the real world. There's a reason for that, they wouldn't work...
And that is one of the criteria I use to decide if such a weapon will be used in a campaign I run. Has something similair been used in the real world? If the answer is no, I'm not likely to allow it. Variations on a theme are one thing, I've designed hundreds of odd weapons. But the weapons I mentioned above are just silly...