The house's floor slab had a crack that wicked up groundwater when it rained too much, so my carpet would get mushy. Electronics off!
The anti-cheat software I ran (PunkBusters) went crazy after an update and banned anybody who connected. I noticed when my MRTG graphs flatlined.
Girlfriend once yanked out the Ethernet cable when we were having adult time. I didn't bother explaining that one to the players.
Heavy web browsing would cause lag, so I ended up learning how to do QoS via iptables (or its precursor, whose name I forgot).
At the time, the server used an astonishing 25 gigabytes of bandwidth a month. Always raised an eyebrow with the ISP tech when I called in, but they never complained.