At my first job, I was having a good old time playing the field with the female co workers. Well long story short, lots of gossiping and other assorted stuff from spurned females lead to me having to meet with the HR director and my boss. Didn't get fired or anything but I knew I couldn't stay there and found a new job. Taught me a tough lesson about having a good time at work.
When I worked for a minor league baseball team, I was in charge of designing the game programs and having them printed. That went fine except for two things. One, I didn't copy edit a story that one of the players had written, and it was full of misspellings (including continuously misspelling his position), and secondly, I was supposed to have the printer print a special code on each copy of the program on a specific ad. Then, on game days, the announcer would call out a number and the person who had that number printed in their program won a prize. I forgot to ask the printer to print the codes, so the finished programs didn't have them. It wasn't until after the first home stand that I realized the mistake.
Got lazy about getting a quote in by the specified date and missed out on getting the kitchen equipment contract for California Pizza Kitchen. Led to me getting canned about 2 months later.
I was an intern for a judge. One of my assignments was to review proposed forms of order that parties submitted after hearings. I read one of these orders, and submitted it to the judge, with the comment that the order contained some of the worst examples of "Texas-speak" I had ever seen. The judge returned the order to me, with instructions to re-draft the form to reflect the ruling announced in court. So I went to listen to the tape recording of the hearing, and discovered that the form of order submitted was a verbatim transcript of ruling the judge had announced in court. Fortunately, the judge didn't recognize or remember the language, and signed the revised form of order without any comment.
Sure... if you like low-paying jobs with little advancement opportunities. BTW, I made many mistakes while there. This was just the most high-profile one.
i accidently rebooted our production server my second week on the job thinking i was rebooting our backup file server (we have this ridiculous 10 port kvm switch and all the desktops look the same and nothing is labeled) and next thing i know is i have the entire workforce banging on the server room door as to what happened...long story short after numerous file corruptions and issues we got it back up the next day after sending everyone home. i lucked out as my boss thought it was faulty ram that caused the reboot since one of the sticks of RAM was bad it turned out after we went through testing all the hardware and not just me rebooting the pc. but yeah i was sh**ing bricks pretty bad that day