A friend was lamenting his weight gain of recent years. And was saying he thought it was time to do something about it. To justify the "do something", he started rattling off a bunch of "you know it's time, when...".
I was amused by some of the items on his list, so, I decided to add some of my own. I'm not sure he was amused when I added, "when your belly button has an event-horizon, it's time to go on a diet."