It wasn't really an accident but back in the 80's I was lying on my back working under the dash of a car and had an array of tools on the driver's floorboard. I had long hair at the time, and moved around to get in a different position and somehow my shoulder hit the trigger on my cordless drill. The chuck was spinning and my hair got caught up in it...hurt pretty bad but it hurt my pride worse when another guy in the shop had to help untangle my hair off the chuck. After that I tied the hair back, but it wasn't long after that I got a regular haircut and ditched the long hair.
In the summer of 2000 I was pushing a small piece of mdf through a cheap table saw and didn't have sense enough to use a push stick. The saw kicked back pretty hard and took my left hand into the blade. It cut off the tip of my left index finger at about a 45 degree angle and took part of the nail with it, and ripped open the side of my left middle finger pretty badly. Took some stitches and hand therapy to get it fixed up, and I still have only a little feeling in those two fingertips due to the nerve damage. I now have the utmost respect for any tool with a blade, electric or fixed.
My own worst one was I had an old 280ZX in the shop when I worked at Circuit City, I was in the passenger side and reached across to turn the key to accessory and the key got hung up in start, and the car was in gear, it was a 5-speed. It started "hopping" forward and before I could stop it it slammed into my old Mac tool box, a bottom cabinet with a separate top chest. Spun the box around and luckily my top box just fell over onto the work bench. It put a huge dent in the side of my bottom box but I hammered it out so the drawers still sorta-kinda worked enough to still use the box. The only damage to the car was a few scuffs on the front bumper cover, which the customer didn't mind anyway. The car wasn't exactly in pristine condition. Luckily, no one was hurt.
One of the worst stories I ever heard didn't happen in a shop where I worked. Some guys at a car audio shop in Gainesville FL built a bandpass enclosure for a pair of subs, in an Explorer or Expedition, I don't remember the car. But a bandpass enclosure has 2 ports, usually 3 to 4 inches in diameter to vent and tune the enclosure to the desired frequency and get more bass out of it at that frequency. Anyway, the customer played it too loud, shorted out the voice coils on both subs and the wires from the spiders to the speaker cones were glowing red hot. The guys who built the enclosure had run out of silicone to seal the enclosure airtight, so they had used Liquid Nail instead. The fumes from Liquid Nail are highly flammable, especially in a small enclosure like that, and the fumes ignited violently, sending 2 columns of fire straight up through the ports in the enclosure in the rear cargo area on the vehicle. It burned the back seat and part of the headliner before the customer somehow got the fire put out, but luckily no one was hurt.
And while I didn't see it happen, there was a guy in my high school's auto shop class that was working under a car that was only supported by a jack. It fell on him, crushed his skull and killed him instantly. That's why I won't get under a car unless it is on ramps or a couple sets of really good jack stands. I always check the car very well to be sure it's OK before I slide under.
Jimmy