The 'final straw' in my case was when I was tooling along a 4-lane street (speed limit 45 mph, but everyone does 55-60), in the left hand lane. The ONLY good thing about that scooter is that it was only a 150cc, but it'd do 60 mph pretty easily.
The engine faltered, then picked back up again, then just died outright. Everything went dead, actually. No brake light, no emergency blinkers, no headlight, no nothing. (Strangely, after it'd cooled down a bit, it started right back up like nothing had happened.)
So, I'm stuck in the leftmost lane, next to the median, and have to figure out a way to get through all those lanes of fast traffic pushing a scooter, to get to the sidewalk. Great fun. Good thing I was only about a mile from home. I once had to push the damned thing 7 miles!