I have fond memories of my dad wiring up a dimmer switch for my bedroom about 35 years ago. He pulled the old switch out, threw it away and then, armed with no electrical knowledge at all, took a look at the bundle of identically coloured wires sticking out of the wall. After a few goes and a fair bit of fuse wire from blowing the fuse box on every failed attempt, he got my light dimming nicely and stepped back to admire his work. It was at about this point my mum shouted 'Why are the lights going on and off?' from their bedroom and it turned out he'd wired the switch to dim the whole of upstairs.....
Much faffing, many hours, and a lot more fuse wire later he'd improved matters to the point where the switch dimmed my room and my brother's room, and he gave up on improving things any further. This despite my brother's desperate complaints and his (accurate) forecast of just how much I'd annoy him for the next decade or so with this new weapon of sibling annoyance installed! An electrician was never called to sort his mess out and it was still the same when we moved house around ten years later.
The icing on the cake was when he went to close my door upon finishing and found that because the door was very close to the wall it wouldn't shut past the dimmer. This last problem was resolved by him fetching a saw and cutting a small rectangle out of the edge of my door so it would pass the switch..... I only realised how odd this was many years later!