This might be a little more than petty.
So this happened when I was in middle school (early 2000s). We had this small lockers with the combination lock attached to the locker. It was standard that students would drop off backpacks in their lockers and only bring the binder or book they needed for that certain class so I would leave my books bag and lunch in my locker during classes. It was common knowledge that some of the lockers could be pried open from the bottom pretty easily (mine being one of them). So at some point of the year someone discovered that my locker was able to be pried opened and would steal my lunch everyday. Being before the time of cameras in schools and not wanting to be a tattle tale there was no course of action for me to find out who was stealing my lunch. After weeks, maybe months of this happening I devised a plan. So that night I went home and made the most delicious looking sandwich. I’m talking the works all the toppings and condiments, of your average bread meat and cheese sandwich. I then proceeded to shave off what pubes I had at the time and hide them under some cheese and condiments in the sandwich. The next day I brought my lunch to school and placed in out in the open in my locker. Not surprisingly when lunch time came around the bag was gone. To this day I don’t know who it was stealing my lunch but I will say that after that day my lunch was never stolen again.