When I was studying abroad, I noticed that the Ethernet at my Uni dorm seemed to have a lot of cross traffic. So I ran a simple password sniffer, not knowing it also effectively turned my computer into a giant switch. Soon after I came home to my flat mates saying “the IT department came and kicked you off the internet.” I thought it was a joke, until I saw I wasn’t on. I called and pled dumb, saying I had installed an “internet accelerator” and they believed me and restored access.

FWIW I wasn’t actually going to do anything with the passwords (of which I accumulated many!). It was mostly just a fun nerd flex with no bad intentions.