I once chlorinated a batch of acetone as a kid, using HCl and Cl2 at around age 13 or so, and oh boy, it got hot, suddenly, and even more sudden was the subsequent flash boiling gout of mono and polychloroacetones instantly vaporising throughout my garage, and quicker still, I am sure, was the aspiring chemist, cursing the air black in several languages, hightailing it out of there.
Another time, wearing the due eye protection, I was performing an electrolysis of molten NaOH, a bead of sodium metal, around the size of a lentil, or so, went 'pop', and left me wondering why no organic chem textbooks ever warn about NOSE protection.
Thats right, I got metallic sodium right up the nose, coated in very hot NaOH.
That one hurt like hell, and left a crater in my septum for quite a while afterwards.
Ring opening a certain lactone under basic hydrolytic conditions again when I was younger, it got hot and flash boiled right at the moment I lifted my goggles to scratch my nose, giving me a blast of hot, saturated NaOH (aq) in EtOH right in the face, my right eye still has poor vision.
Immediately ran to the sink and irrigated my eye and the rest of my face, then spent the next several hours pippetting up product from the floor, sink fittings, and swabbing splattered lactone and NaOH mix from the walls, floors and ceiling, aside from what was left in the flask, quite a lot, I did however manage to recover several hundred grams of perfectly useable product, which in more than one way left the night with a good ending (apart from the 'owwww shit' factor.
Scratching ones family jewels after working with KMnO4 is also not to be reccomended.......it leaves brown MnO2 stains that cannot be washed out, and it burns like fury for about two days.
I once, in my younger days, dissected a load of batteries I found, really large, unusually so, lithium cells, with a central pin type structure I assumed at the time to be some sort of pressure relief, upon yanking it out with pliars, and peeling back the casing, in the process I got my hands covered in what I assumed to be liquid SO2 at first, or something like it, then soon after kicked myself (metaphorically) repeatedly up the arse, finding out it was almost certainly thionyl chloride.
Stuff rotted my leather gloves to shreds in just a few minutes after contact, I didn't get too much trouble for it, aside from a permanent thickening and scarring of the skin on a large part of one hand and the utter and absolute destruction of a really nice pair of steel-spiked leather gauntlets (the spikes of which incidentally rusted up within a day or two.
Other accidents, misc. mishaps:
Small white P burn on one wrist, hurt quite a bit, maybe about the size of a grain of rice worth of phosphorus found its way onto my hand distilling the white P, formed by heating the red allotrope, didn't think much of it at the time, other than a minor burn hurting like one does, although later that hand became so weak, it became absolutely impossible to hold a pencil, I didn't at the time connect the two, until a short while later, when I remembered the burn.
Produced very pronounced localised muscular weakness, which surprised me, I haven't before heard of P burns having this effect, although I am well aware of its toxicity, I couldn't grip a pencil and write, trying to, my hand shook like a parkinsons patient with the effort, before just giving up.
Small scale Cl2 inhalation, didn't cause anything worse than gagging.
Likewise with SO2, although I actually like the smell of burning sulfur quite a lot
Some would hint that it implies certain things about my....parentage :p