My (former) best friend who stole and hid my wallet which contained my documents on a school trip in another country because she was jealous I was starting to befriend new people (I met a few girls on the trip who were from my school as well but attended in another school building), she slipped it one of their backpacks (to frame the girl, I presume). I, a 12 year old at the time, almost ended up being stuck in a foreign country.
As, if that wasn't enough, before it came out that she was the one who had hidden the wallet, we were together in the city's main street (our teacher took us there to do some shopping) and she suddenly decided it was a good idea to storm off (after a minor argument over Chicken Nuggets) while I wasn't looking. I obviously refused to talk to her for the rest of the day and it was pretty safe to say that our friendship was over because several other similar things had happened.
You can imagine my shock when I found the wallet and the story behind its disappearence.
When we got back to our country she told everyone (teachers included) that I had made it up and that I was the one who had left her all alone (because I had refused to speak to her) and obviously the people who bullied me at the time took a liking to this story and yeah... that year was a pretty shitty one.
Perhaps it's petty but hey I was 12, and I feel like my pettiness is a little justified.