I have a million of these because for most of my young life I was a real piece of garbo. I've already talked on here once about my ghostbusters thing so I won't go into that again because it's in my post history but here are a few choice examples:

Had my lab partner completely convinced marshmallows were a special kind of sap harvested from exotic trees.

Many grievances against my sisters including: Convincing them that milk containers at dairy processing plants contained cows stacked vertically (complete with sound effects while we drove past) for many years, ghost living in the attic (me), and that my father had another family

Developed software for the express purpose of cheating in Runescape and then sold both the software and the rewards won by the software. Not my best moment but not quite as bad as

Bought herbal smoke alternatives off the internet and fumed them with liquor and wormwood and sold it to my high school aged peers as weed.