I know that there is a thread that has the funny stories, but I wanted to find more about the bloopers of cos/crossplay!
I actually didn't know I had already cosplayed... It was when I was about twelve and Mortal Kombat came out for the Super NES. I got a hold of my moms sewing machine and made a Scorpion outfit... hood and everything. I didn't have any thing to make a skull face, so I used some fairly thin black cloth and painted a skull on it. The oversight was that the cloth was only see-through in bright light... My buddy(dressed as a ninja) was over and we were sparring in the machine shed by my house and whe he ran around a corner; I followed, but didn't see that there was a shelf just my height.... Lets just say that my feet went farther into the room than my head... Luckily the mask was fairly thick, it didn't do much of anything but scratch.
....I don't think that I was knocked out until my head hit concrete floor, but it was only for a short time... My buddy said it was cool how I flew through the air and hit the floor; "JUST LIKE THE MOVIE GUYS WHEN THEY GET SHOT!"