These are some things I found from another site. I'm sure you guys can add to this.
Never leave the chuck key in your drill press chuck. Nuff said.
The best shop tool blunder I have ever seen was when one of our drivers put a piece of angle iron in the drill press vice and didn't clamp down the vice. I made it all the way to the hospital 30 miles away without saying I told you so. Two casts, 13 stitches later it was not funny. To this day he wont use the drill press.
Don't use a bug bomb without turning off the water heater!
Don't spin your wheel bearings with a blowgun when you blow the solvent off of em. The resulting explosion will tear the heck out of your fingers. Sure, it makes a neat sound, but don't do it
"Do not" remove stop block where mom knows when to stop when backing in the gerage.... had to explain to my old man why beer fridge is sporting a half caved door and moms 96 Couger has white paint on rear bumper......
Don't try to install struts without a compressor - it's like the 4th of July when those suckers let loose, and the hood will never be the same.
Never back your truck into your garage with the drivers side door open. If you do drive your truck into the garage with the drivers side door open, don't give it more gas when you need to get it in that last foot...
Do NOT use a 9in grinder on steel when there is a truck battery hooked to a charger 15ft away....
BOOOOOOM!!
I was in the other workshop under the hood of a LandRover, heard the bang & then heard things hitting the top of the LandRover. It was parts of the battery case & lead plates.
I walk around the wall to find the battery is now U shaped with nothing in the middle at all & just the 2 posts sticking up with 3 or 4 plates attached to them.
At this point the (Welsh) owner of the battery walked up, looked at the damage & said "So, will it still hold a charge then boyo?"
Reply: "Doubtful, it won't even hold water you thick git".... LOL!!!
This reminds me of the time I helped a less than mechanicaly inclined friend jump start his Pinto. He drove a big dump truck for a living and asked me to get in his truck (because it had a TWO REAL BIG BATTERIES), and drive his Pinto back after he got it started. Upon getting there, he drug out some jumper cables, and hooked them up. The Pinto battery must have had a dead short inside, nothing happened. My friend said he never saw a car his truck could not start. Then he said, "mabye if I swap the leads." I told him he had it hooked up right. But this guy was not listening to me. As I tried talking him out of it I walked backwards, out of range, I know something real bad was going to happen. It did, BOOM!!! I looked at the pinto's ex-battery, it was now an empty plastic box, 4 sides and a bottom. Everything under the hood of the Pinto was smoldering with battery acid. Then I looked at my friend as he pulled his hands away from his face. Lets just say it was not a pretty sight and medical attention was needed. Lucky for him, the house the Pinto died infront of had a water hose out front, and my friend had enough sense to close his eyes before doing the unthinkable.
And always clean off all the tools from the top of your engine before starting it.