one time i was fucking around with local network things trying to do funny things with connections that came from a game console (notably a machine that i own but don't completely control the same way i do a pc). and i never got them working. and then like 4 hours later i was lying in bed and i realized "it's probably good that couldn't get that working, i was trying to perform a mitm attack"
i had a goal in mind and it hadn't occurred to me that i just took a back door to reinventing exactly the thing that we have ssl to prevent
i've done a lot of local networking fucky stuff, just for fun. and almost none of it has ever worked. but i've done my fair share of "connecting a laptop to my desktop over ethernet and sharing the wifi connection to it so i could sniff packets" etc
you used to be able to take an egg from a gen 6 pokemon game, start an online trade, try to trade them the egg, and cancel it. you could sniff the packets from the trade to learn things about the egg, and do some math to find out what trainer ID someone would have to have to hatch the egg as a shiny. then you find someone with that ID and trade them the egg, have them hatch it, and trade it back. cool stuff
unfortunately you could do the same thing to cheat at battles because the game sends your opponent your move the moment you click it, so in a patch they encrypted all the communication. very sad