Dumbest thing I ever did was delete the default route on a friend's machine that I was adminning while he was out of town. The machine was in New Jersey; I'm in South Carolina, so obviously I couldn't exactly just drive up and fix it. (Especially since I couldn't even drive at the time. I
still can't, actually...
)
I don't remember
why I did it, or why I was even messing with the routing table at all. I just thought, "okay, need to delete the default route and readd it ...
route del default, then
route add default gw ..." ... I got up to about 'rou' and then the machine realized it didn't have a default route and stopped talking to me. And then about five seconds later I realized what I had done.
Needless to say, that's one mistake I'll never make again.