I dunno if this is the stupidest, but it's up there.
I decided it would be a good idea to ride this thoroughbred (racing horse) on the trails when the girl who rides the horse only ever takes him on the trails to gallop him. He took of on me and I decided I would jump off so he would stop and hopefully it would prevent him from hurting himself. I jumped off right at the place that was littered with rocks. The horse didn't stop, it galloped all the way home.
Anyways, this is when I was like 14, hopefully I have learned better judgment since then. What is the stupidest thing you've ever done?