I once saw a soap dispenser which had gotten stuck in a loop.

If no one caught the soap, it fell past the sensor, triggering another soap release, and so on.

I'm sure it was a special case, some obscure failure of the repeat-dispense lockout or something. But I couldn't help marveling at how much effort had gone into making such a singularly crap product; it was behaving worse than would even be possible for a lower tech device.

Reminds me of this marvel of modern engineering: http://imgur.com/Na9jGYR

I drive past a spotlight every day on my way home from work which just flashes on and off the entire time. I'm quite sure it's because the dusk-to-dawn sensor senses dark, turns on the light, which then hits the sensor and turns it off again, ad infinitum.