parts wearing out

The surest way to realize that you're getting older -- that your body is getting older -- is to inexplicably injure yourself doing the exact same thing you've been doing every single day for years. And I'm not even talking about one of those crick-in-the-neck sort of things you feel when you wake up some mornings, but rather the type of injury that sneaks up on you one unremarkable afternoon and makes you say out loud, "Ooh, that smarts."

Better yet, make it a slow-healing injury that disrupts everything -- the way you work, the way you sit, the way you drive a car, even the way you sleep. But absolutely, absolutely make sure it has no outwardly visible symptoms. That way, you can surprise even yourself with just how fake your excuse sounds when you say, "Sorry, I can't help you with that right now on account of my injury."