Broken UFO parts
Embed numerous "repulsor" coils and a power supply in a small, fake UFO crash remenant, so that small independant segments of the object hang unsupported in the air nearby, via the battery-powered "Meissner effect" generator. (independant segments must be magnets, of course) Take it to a mainstream researcher, but don't let them look at it in detail. Visions of alien room-temp superconductors should haunt the person forever after!
"Stink Beam" projector
A large, hollow-ended cylinder is attached to a bass loudspeaker. The open end of the cylinder is covered with a flat plate, and a 3in. hole is put in this plate. When a pulse is applied to the speaker, an invisible ring-vortex or "smoke ring" of air will be launched. Pulses can be repetitive, so a continuous beam of vortices is projected. Pulse waveform can be tailored to produce robust, fast, silent vortices. Each vortex incorporates air from within the cylinder, and carries this air along as it travels. If a scent is placed in the cylinder, you have a "stink gun" which can target a distant nose without being intercepted by others, or can surround a distant object with any desired scent. If specific gases are added, then when the "stink beam" encounters a distant source of ignition, such as a cigarette, the vortices (and maybe the launcher device!) will explode. A computer, video grabber, IR camera, and some stepper motors could be assembled into a cigarette-targeting acetylene launcher. No Smoking!
If a sharp point is attached to the dome of a VandeGraaff generator, the point will spew charged wind. If you stand in this air stream, it will charged your clothing and hair, which will start clinging to your body. Ewwww!, feels like you've been dipped in vegetable oil. So, bolt a VDG upside-down within the ceiling, with ion-needles pointing downwards, and a "stand here" sign on the floor below. (only works in fairly low humidity, the lower the better.)
Free energy" hoax
Fake device is composed of complex structures and materials, a tiny battery-powered spark generator, and at a distance, a hidden, "stink beam projector device" rigged for acetylene. The projector shoots gas pulses which cause occasional loud and unexplained explosions within the device. If both an ion projector and an acetylene launcher are used, it may even be possible to create sparks and explosions in a distant device which contains no power supply at all!
Use my whitelight abrasion hologram method to encode an image of Elvis or other religious icon holographically into an everday surface, (car hood?) Announce the miracle, charge admission, and even befuddle the experts who come to debunk it. Impossible!, a real hologram, but encoded into a crude painted surface!
Roadside Kilovoltage Source.
Build a sturdy VandeGraaff generator into a metal and plastic column, with a handcrank on the top metal terminal and a large lable saying "TURN." When the crank and stepup gearing is turned, the generator operates. Place it outdoors, and surround it with a thick plastic insulating plate. Anyone who cranks it will feel a prickling sensation, their hair will stand up, and the next person they touch will get a huge "static zap." Better still: win the lottery and have thousands of them built and distributed around the country unannounced. Permanent Infamy!
4-Lane dot matrix printer
A truck-mounted device spits a row of paint dots under computer control. Drive along the Interstate while printing out political diatribe. Use water instead of paint for temporary, less illegal road gibberish. Colored dyes would work well on packed snowy roads (a little carbon copier toner or flourescene dye goes a long way.) Rent out ad space in fields near airports, then do your printing in seeds for variously colored crops. Transport one of these devices between widely-separated power boats for the seaborne version. Electrostatically shoot charged copier toner from lunar orbit downwards for a more noticable and long-lasting advertising sign.
Ed Harris on usa-tesla has discovered that argon gas lets you make a large 'plasma globe' effect at ambient pressure. Build a battery-powered Tesla Coil, clip it to your belt, and run a wire out to an argon-filled mylar sphere. When turned on, the tip of the wire will grow a large blazing white ball of lightning filaments. Run screaming through the night, chased by a ball-lightning in a hardly-noticable clear bag. Charred, smoking clothes would be good too. Ahhhhhh! It's biting me!
Build a Borg
The Yale psychologist Stanley Milgram discovered a strange group-organism he dubbed the Cyranoid. Build one as follows: provide one person with a radio receiver and earphone, give a transmitter to a second person, then have the 'sender' give orders which will be carried out by the 'receiver.' Even better would be a video RF link so the 'sender' can see and hear through the 'receiver's' eyes, and maybe add a radio channel which controls vibrating transducers on the 'receiver's' body, so that the 'sender' can command movements with a joystick rather than verbally. If one 'sender' runs several 'receivers,' you've got the start of a small Borg civilization! Would you pay more to be a sender or a receiver? Should be great fun at parties...
If pure argon is injected into a laminar stream of air, the argon stream will support sparks of enormous length. If connected to a fair-sized tesla coil, the argon stream should produce linear arcs many feet long. This would be easily disrupted by wind or by a small fan. Indoors use only? Reach out zap someone! A similar effect can be had by running an argon stream through a hose connected to a distant tesla coil. Hot dangerous arc-plasma will pour from the hose end. "Don't unplug that hose, it's not full of water!"