While everyone is sharing funny stories, I'll share one of mine...it didn't actually happen to me, but it was pretty funny still.
OK, so, my sister and her friend were all dressed up in goofy dresses and some high heeled shoes. I was heading back down the stairs with them (they had gone up to show my Mom how funny they looked). So, we get to the bottom of the stairs and my dog decides that she wanted to come. Now, my dog doesn't just walk down stairs, she throws herself down stairs. So she comes throttling down the stairs at full speed and I managed to get out of the way, but the stupid dog ran straight into my poor sister's friend, who then did a complete backflip and landed on her back, wondering what just happened.
She did a full-on cartoon banana-peel fall, too. XD It was really funny.