Good post title, BrokenHalo.
I'll chime in with my two.
1987, my first full time job. I was a small ISV's UNIX guru. I wanted to remove everything under /usr/someone. I cd'd to /usr/someone and typed, "rm -r *", then I realized, hey, I know that won't get everything, better add some more, and the command became, "rm -r * .*". I realized, oh, no, this'll get .. too, so I better change it to: "rm -r * .?*". It took about 12 microseconds after I hit enter to realize that ".?*" still included "..". Yes, disastrous results ensued, even though I was able to ^C to avoid most of the damage, and I had the backup tape (back in the day, we used reels) in the tape drive just as users (other devs) began to notice that /usr/lib wasn't there. Yep, I have my own memories of red-facedly telling my boss, "oops, I did this, I'm in the process of fixing it now. Give me half an hour." In the future, "rm -r /usr/someone" did the trick nicely.
Early 1990's, I was consulting in the data center of a company with 8 locations around the world. It contained the company's central servers that were accessed by about 700 users. Being a consultant, they didn't have a good place to put me, so I ended up at a desk in the computer room. Behind me was a large counter-high UPS that the previous occupant had used as somewhat of a credenza, and I carried on the tradition. That is, until the day I had put my cape on there, and the cape slid down and through one of those Rube Goldberg miracles caught the UPS master shutoff handle, pulled it down, and I heard about 30 servers (thank goodness there weren't more) powering down instantaneously. Amazingly, I lived, based on the ops manager pointing out to the powers that be that it was a freak accident and that others had been sitting similar stuff in the same place for years. The cape, however, was not allowed back in the data center.
Fortunately, I've had better luck and/or been more careful over the past 20 years.