When I was about 5 years old, I found a nickel and put it in my pocket. When I went to bed that night I put it in my mouth (yeah I know... dirty) and it got lodged in my throat. I couldn't cough hard enough to get it out and I literally started hitting myself in the chest and coughing as hard as I possibly could, dislodged it after about 20 seconds or so... almost killed me.
edit* also random somewhat related... You know the large stacks of CDs/DVDs you can buy that come on a spindle. Well there is a CD shaped piece of plastic, it's a lot less rigid and thinner than a CD. Anyway I was busting it in half over and over again out of boredom breaking it into smaller pieces... well one of the pieces flew up and pegged me in the eye... had it of been harder plastic I would have lost my vision... it's crazy how one stupid mistake can cause catastrophe...