Although I've never broken a bone, I have my story ready if my streak of good fortune ends: "I was skiing a double black diamond on the Swiss Alps when I swerved to avoid what looked like a Yeti."
Admit it, aren't you dying to hear a good story when someone you know turns up in a cast? Aren't those stories about tripping on a toy, etc. getting old? Who gets hurt if someone tells a whopper, at least as the first response to the inevitable "What happened?". I say let the truth wait for 5 minutes so that everyone, fibber included, can experience a vicarious thrill. I will not be offended if you fib, provided it's a good one. FYI, I like stories involving wild animals.
Think of this as a way to manifest some dormant creativity. And don't wait for the accident or mishap - start inventing some good stories now so you're ready and appear credible. Because you know people are going to ask. Now about that scar on my neck.