My mum had a friend who had a son a few years younger than me. When Mark was about three, he happened to be passing the fuse box in the under-stairs cupboard and "helpfully" turned on the main switch that the electrician had turned off while he was working on a circuit. The electrician (who lived at the house which backed onto ours) survived unscathed, but he was not best pleased!
As an aside, mum's friend used to complain that if I was left alone at her house when I was little, I'd get up to mischief - pouring salt into the sugar bowl, screwing up (literally!) the tension on her sewing machine, spilling her perfume on the dressing table taking the varnish off the wood, etc. Then when her son got to the age I'd been, *he* started with pranks - I know he put a stick in her twin-tub washing machine, jammed the paddle and therefore the motor and caused smoke to come out of the machine; and there were many other things. So she had to admit that it was not just me but "all" boys who got into mischief at that age. The one that took longest to diagnose and fix was probably a genuine accident: he was playing in their car and accidentally dislodged a wire under the dashboard with his foot (though no-one knew that at the time), causing half the electrics to fail - not irreparably, but until the wire was found where a plug and socket had been pulled apart.
Now tell me that girls *never* do that, ever ;-)