Found a good one yesterday.

My parents told me that their outside light had stopped working, and was tripping the circuit breaker for the lighting circuit.

Simple enough, I say, as there's only about six feet between it and the light switch which it works from.  Probably just a bit of water having got in somewhere.

You can imagine my surprise when I pulled the light switch off the wall and discovered what it had been wired up with.  TV ANTENNA COAX!

Even more surprising is that it had been working perfectly fine for at least the last eleven years since we moved in.  Unsurprisingly, the cable was a dead short and the cause of the tripping circuit breaker.  It's now been re-wired with something rather more suitable.

I've done/seen/heard about  a few interesting ones:
once, when I was about four years old or so, I attempted to stick a nightlight bulb into a regular lamp. Oh, the sparks! It destroyed the lamp!
Don't even get me started on Nitwit ridge!
I've seen wiring connected to a generator with absolutely no breakers of fuses.
My friend's house had/has (note: we are off the grid), a 2-prong plug powering the house!
Someone I know has wires SCREWED into other wires (note, this is 12 volt ), and disconnected.
My neighbor's house was pretty crazy.
I have seen extension cords used for actual wiring.
Not as bad, but my school has mixed-up color temps of flourescent lights. It's kinds weird to see one chroma 50 among a bunch of 4100k tubes. They also don't change both bulbs in a fixture at the same time, so you have mixed brightnesses.
My teacher related a story to me of his son putting a piece of paper in an easy-bake oven, it almost caught on fire.
My teacher has been jokingly called an electrician when working on cubicles with integrated wiring.
Someone I know tells a story of the plug for a stereo being halfway out of the outlet but still making contact, when a necklace fell from the shelf above the sparks were pretty awesome, evidently.
Let's not forget someone I know who had a breaker box mounted to their generator. Even though there was a big piece of rubber between it and the box to absorb some of the vibration, the wire for the main breaker vibrated loose and arced. Ever since this individual had lived in that house, the lights had flickered slightly,but it suddenly got worse one day. Guy goes into the 20' container van the generator was installed in, and the room is full of smoke and the burning wiring smell. He immediately shut off the genertor, and discovered the arcing, which had melted the breaker!

I've seen wiring connected to a generator with absolutely no breakers of fuses.

I think AFCI is a uniquely American thing, as here 230V will trip breakers.