Dating myself but as an inquisitive and (I thought) tech literate teen with a Linux box (an early version of Slackware) I graduated from running an old school BBS into the grand world of the Internet. I'd gotten my own phone line for the BBS as a birthday present q while ago and once my dad got Internet access I was ready to explore this new world. This is in the very early days of the WWW, and having home internet access was still very unusual. (My dad needed it for work, he was in the tech industry so every year or so I'd get his old computer when he upgraded, I had a shitton of computers running Linux, Minix, Xenix, a Sun box, and other random shit all on a LAN. Fun times.)
There was an extra phone line and an extra ISP account so I rigged up a little bash script to automatically reconnect the dialup internet connection when it dropped (and it would drop a couple times a day, it was SLIP, I think, this was possibly before PPP was a thing), it would even try to dial one or several phone numbers the ISP offered. This, with a static IP address, allowed me an ersatz dedicated line. I ran an IRC server and a site with a bunch of edgy shit about drugs and stuff like that.
Unfortunately there was some kind of fuckery with the phone company, they'd recently changed something with the area codes where I was living (my memory is fuzzy) and our phone number changed and you started having to dial all ten digits of phone numbers regardless of the area code but anyway one of the phone numbers became a long distance call when it was not previously. This didn't occur to me and the script kept doing it's thing.
This resulted in a phone bill for my dad in the neighborhood of $6,000. Needless to say he wasn't happy. He banned me from running the script but he was fortunately able to negotiate his way out of the bill with the phone company so all was eventually good and I started running the whole thing again. Very carefully.