The world is rife with mundane crap that doesn't qualify as even remotely lethal, and that's barely hilarious at all. Fortunately, with some moderate tweaking, even the simplest of items can be turned into something horrifying.
Just ask the inventors of the...
7Super Soaker Flamethrower
When Super Soakers arrived on the scene, they put ordinary squirt guns to shame with their extended range and awesome power. Sure you had to pump till your arm cramped into a freakish, bent claw, but that just prepared us for many lonely, cold nights in front of a glowing monitor.
It was only a matter of time before some disillusioned youth with pyromaniac tendencies and a fascination with WWII-era weapons of horror noticed that water wasn't the only thing you load into it. And where more wholesome youth would have stopped at firing delicious nacho cheese from their squirt gun, others were determined to turn a water-soaked afternoon of fun into a fiery nightmare of unsupervised hooligans and singed eyebrows.
Super Soakers have ranges up to 45 feet, meaning when you set one ablaze you can torch your neighbor's house from the convenience of your own kitchen or barbecue their hot dogs for them without having to stop watching Maury.
The Internet offers up a wide range of videos on just how to make one, with some budding young arsonists and future burn victims choosing to rig up an ignition system while others simply get a friend to hold a lighter under the flammable stream (because there's probably no way that could end badly).
Though if flaming guns are too modern and crass for your tastes, you can always burn yourself the way our forefathers did by wielding this guy's flaming sword.