It's when the stupid network goes and dies on you, just before you're about to log-off.
Because this leaves you with the problems of:
1. Being unable to look at any sites, and
2. Being unable to log off.
And the system we have at my college means you have to log-off when you go offline. Or else demons will come and eat your Internet Quota.
So, I have spent the last half hour sitting here, waiting for the network to repair itself, just so I could get offline.
And it still used up some of my quota.
Dear Network Admins,
I would like to introduce you to a friend of mine. He's named "Logic." Now why don't the bunch of you sit down and get aquainted, huh?