Oh man there's so many stupid things I've done to Amigas over time!
I read something about powering an A1200 Motherboard via the floppy power supply header, so I merrily connected an AT PSU and it surprisingly worked. However, the sound output wasn't working properly so I realised it was a bad idea.
Amazingly, the A1200 sufferred no ill effects.
The other silly thing I did was to ignore the slightly strained sound from the chip fan attached to my overclocked '040. One day it detached from the chip and since then I'm presented with a red screen every time I turn on my machine.