Most of the actual electrical stuff isn't so funny or too memorable - the other type of finds are....
Dead (decaying) rat latched on to chewed and shorted NM inside a wall - same for squirrel. Various dead mice.
Horribly misused extention cords. Not so funny - but hillarious what people think can be done with them. As well as other laughable wiring methods too numerous to list.
All kinds of nasties found in J-boxes. Hornets - no thats fun. And slugs, (Cousin of snail - not to be confused with KO slugs) found a christy box full of them once. Black widow spiders. Panel full of roach bodies - I broke open a breaker in that same panel to find it packed so full with roaches that I beleive to caused its failure to operate.
Other than just historical ditritus left in crawl spaces, like 1800's shoe shine kit, pottery and plate chards from the 1906 quake - melted bricks from same. Cold medicine from 1928. I found several pages of newspapers of various dates. One from the 30's stating that "war in europe may break out any day now..." Had a helper run into a hibernating rattle-snake - that was fun....
And my all time kicker - a whole bar hidden under a house in the Fillmore district of SF. Due to the hidden entrance - possibly a forgotten speakeasy from prohibition. The owner for over ten years had no idea it was there until we tried to drive a ground rod in the garage and it dropped though to this hidden room. I have learned that they subsequently had to do major foundation work due to this neat little addition. It is now ironicaly a wine cellar and still has the same bar newly refurbished.
"Well - I oughta....." -Jackie Gleason