When I was in my 30s and working in a restaurant. Behind the staff counter was an under-counter cupboard with keys hanging on the inside of the door. One of the keys was for the cupboard that had all the spare stock, like mugs, napkins, etc.
The key was quite small and very slim. I had to go to the stockroom for something, and as I was really busy dealing with customers and doing a load of other stuff, I quickly shoved the key in my shirt pocket with the intention of putting it back on the cupboard hook within a couple of minutes.
I completely forgot about the key!
Went home, shoved my white shirt, white t-shirt, and black trousers in the washing machine. Back to work the next day, and the staff were panicking because they couldn't find the ONLY stock cupboard key!. That's when I remembered it was in my shirt pocket, being washed!
There's no way I'd confess, as our boss was an evil witch and nobody liked her; she was controlling and awful, walked around with her nose in the air, barking orders. Even though I genuinely forgot about the key, she'd have sacked me on the spot and would have had me hanged.
The second I got home, I grabbed the key and put it in my purse, then, very sneakily, quickly put it back on the hook as soon as I arrived at work .... and I was the only one there at the time, so there were no witnesses!