Well not so much stolen but temporarily availed themself of the use of my toothbrush.
Worked at a law firm, and we had a unisex toilet (small office). In the cupboard in the loo, I kept a toiletry bag that opened to reveal two see-through pockets with spare knickers & sanitary towels one side and toothbrush /toothpaste the other.
One day I was off out and decided to brush my teeth, when I opened my toiletries bag, my toothbrush was wet, and it had been shoved in the knickers side, leaving a toothpaste skid mark along my clean knickers.
This kept happening despite me putting big notices on my bag and telling the un-named culprit off in our team meeting.
The culprit did not confess nor did they stop (I only work with men). So I cleaned the toilet with my tooth brush and put it back in my toiletries bag and at the following meeting I announced what I had done. I had no shame!
I subsequently found out it was the senior partner brushing his teeth before a client meeting! Oh joy!