I was borrowing my parent's speakers until I bought a pair of my own. Having no need of their speakers, I plugged them back into their computer. When I did so, my internet went down and it took me a good 10-20 minutes to get it back up.
I'm not a dumbass, I didn't unplug anything or try to stick the speaker jack into the ethernet cable jack, nor did I touch the modem or the wireless router.
Might just have been a coincident that it went down at that exact moment, or you could have accidentaly touched one of the wires so something went wrong. I think the first option is the most likely one though.