This isn't my worst pain, but it was close to becoming a really bad pain.
My friend and I put thumbtacks inside of nerf darts, and we test shot them in the backyard.
Once he left, I forgot to unload one of the guns, and when he came the next week, he thought the gun was unloaded (We always do this thing where we scare each other by pointing the gun at one another at random times, then pull the trigger, and we always think the gun is unloaded, but this one was.), so he aimed the gun at me, I shouted "NO WAIT ST-" and he pulled the trigger. It hit me in my shoulder, and almost struck my neck.