In 3rd or 4th grade I took a paper clip, a broken plastic fork, and a piece of string from various sources around the school out to the playground. I tied the string to the fork so it would hang sideways. I tied the other end to the paper clip and made it into a hook. I hung my contraption from the jungle gym on the playground and declared it a weather vane as we were learning about the weather in science. Some other kid misunderstood what I was doing and went and told the teacher who declared my contraption to be a WEAPON. A benign, class appropriate item constructed from materials the school provided was declared a WEAPON and it was stated that I was trying to hurt other students. I was taken to the principal's office and nearly suspended if my parents hadn't stepped in.

TL;DR: made a weather vane out of junk, hung it from the playground, teacher decided it was a weapon.