I was frustrated that it would take 1/2 hour just to get my emails and resorted to unplugging the offender's cable from the router. My emails would come through in about thirty seconds and then I would replug the cable. The offender rarely noticed these 30-second drop-outs.
This created another problem. Because some industry idiot decided that RJ-plugs would be acrylic rather than nylon, the retaining catch is very easily broken off, even when protectors are in place. So I resorted to sticking a spare line-power switch into his cable.
Because it was a two-pole switch, I selected the positive and negative data lines to interrupt.. All that was required was to open up the insulation until there was enough to cut the solid orange and green lines and connect them to the switch terminals, then re-assemble.
This is not a highly detailed i'ble because it had already been done before I discovered Instructables but, I think it's simple enough for people to get the idea.
This switch also made it convenient to disable the offender's computer when he was supposed to go to bed. One flick, and no access. I could have selected only one data line but, as mentioned above, it was a two-pole switch so I chose both data lines.