I used to work in a primary school office as admin. I was young, it was my first job and I was only a trainee. I was staying behind in the office doing something, (Principal and other admin lady usually left before me) and also using the internet (which I shouldn't have been doing but the internet was a new thing in our small rural area and I didn't have it on at home) and the cleaners wouldn't be there that afternoon so the Principal asked if I could lock the doors on my way out. I got so caught up on looking up stuff on the net (screensavers IIRC - it was the late 90s, I would download them on the floppy disks and then load them onto my home computer - games, wallpapers, stuff like that) that I forgot about the request and left sometime after 5pm went home as usual and left the school office door/s open - meaning files, computers etc left accessible.
I got home about 5:30pm and mum had dinner ready at 6. I took one bite out of it and suddenly realised I'd left the school office completely open and unlocked. Told mum I have to rush back to work and put my plate in the oven, took off and made it there in 9 minutes by speeding, it's normally 15 mins drive. When I got there, door had been shut and locked. I drove back home (normal speed) and could barely finish my dinner as I was worried about what would happen the next day.
Next morning, Principal asked to speak to me and I told him what happened, that I had honestly forgot - rushed back and it was all locked up. Transpired that another teacher who was doing work in their classroom noticed the office was left open and unlocked and locked up for me, but told the Principal. He wasn't impressed, more so because I had stayed behind mucking around on the internet and had somehow accidentally set the screensaver of the computer I was on to a Freddy Kreuger screensaver! (I remember looking at it, but not setting it). Yikes! So that was a double fuck up.
From then on, I had to leave work at the same time the other admin lady did....

Luckily I didn't need a reference for my next job.