3 Shockwave Generators
Any self-respecting evildoer eschews standard firearms for both himself and his minions. No, a truly sporting field weapon must be so unconventionally bad-ass that it will backfire and injure everybody within a 5-yard radius. This is why bad guys prefer death rays, exploding boomerangs, and vuvuzelas that shoot swarms of bees. Or, say, a comically huge gun that shoots invisible shockwaves that can knock down entire crowds at a time.
It can only be voice-activated by maniacal laughter.
In real life, they call it the "Thunder Generator," and it's a (mostly) non-lethal Israeli weapon that sends out a series of loud, knock-you-on-your-ass shockwaves. We're talking 60 to 100 per minute at a range of 50 meters, though tests show they can boost that distance up to 100 meters. It's similar to a very loud speaker, only it feels like being in front of a firing squad.
The Thunder Generator is basically a small, rapid-fire vortex cannon, similar to the ones farmers (and the occasional auto manufacturer) fire into the atmosphere to try and disrupt hail storms. Science says that doesn't work, of course -- at those ranges, firing shock waves into the air doesn't do anything except make loud noises. But if your target is close enough, a vortex cannon can do some damage. Here's a video of one knocking over a stack of bricks.
"Eat that, High Middle Ages!"
The Thunder Generator was originally developed to scare birds away from crops and airports, but it has been modified to deal with human threats. And "non-lethal" is a loose descriptor here. The designers freely admit that, at 10 meters or less, the sonics will kill you deader than shit.
But rapid fire and non-lethal lethality aren't the only things this baby comes equipped with. They can affix a curved barrel on these beauties to shoot around corners, too. Ha, those bastards won't even know what's coming. They'll just be marching down the street when WHAM!, an invisible punch knocks them on their ass.
This replaces the older method of playing Adele songs until the enemy was subdued with clinical depression.
Though if it's pure psychological terror/confusion you're going for, then you'd probably want ...
2 Sonic Black Holes
Even at its most silent, our world is brimming with ambient burbles and murmurs. Now imagine the chaos that would unfold if one mad genius held all the sound in a major city hostage. Discotheques would shutter, Harley riders would cry tears of silent frustration, and stand-up comics everywhere would resort to miming and smashing watermelons with oversized mallets. Indeed, this is the dystopian reality Israeli scientists seem to be working toward with their sonic black hole.
Humans have made your standard, matter-gobbling black holes already, but those little bastards are difficult to manage. So to better understand these mysterious maelstroms of cosmic destruction, scientists decided to create a safer, more playful version.
"No, it's safe. We put a sign on it, see?"
By chilling 100,000 rubidium atoms and using lasers to create a whirlpool effect, scientists were able to create a sonic black hole from which no sound can escape. It apparently works just like a regular black hole, but for noise. It absorbs bits of sound -- or "phonons" -- just as a black hole eats photons.
So what possible use could this be in the real world? Well so far, scientists have only maintained the effect for a few milliseconds, and they plan to use this auditory abomination to study real black holes. This is because they have no imagination. Though, if someone built a device that devours all sound and they planned to use it to blackmail the world's richest teen pop idols, do you really think they'd admit it? Or even worse -- what if some dastard purloined this technology and trained ninjas with black holes strapped to their backs? The mind reels at the possibility.
Soon, men and women begin using them against each other. Within days, the entire planet is at peace.