Whacking mailboxes with baseball bats is a regional sport here. It's the same ol' same ol' - --- kids with nothing better to do, driving around late at night looking for trouble.
Though I once accidentally "offed" someone's mailbox. One of my schoolmates let me ride her pony one day, and as I rode by one of her neighbor's mailboxes the pony bolted and she brushed against the box and her tail got snagged on the post. She took off with me --- and the mailbox dragging from her tail down the road. Of course the box dragging from her tail and the noise it made made her panic more.
I was bareback so all I could do is wrap my legs around her and try to rein her in. I can't remember how I finally stopped her. But I unsnagged her tail, walked her back carrying the mailbox and post, and stuck it back in the ground where it got pulled out. It was suprisingly only slightly scratched, so I kind of tiptoed away and until BYC it has been my evil secret for more than 40 years.