I have two, first one is hiding. Pretty standard. I have a desk with one side next to a window, so I could slip down there, and hide whilst also waving at people on the top deck of a bus in order to get help.
I really hope that I'm in the toilet when it happens though. There is a panel which I could get through in the celing. I'd wrap my tie around my head, and kill the fucker, rambo style. I'd go through the duct system, then bust out and drop on him, disarming him, and winning the affection of the one hot girl here. That's going to be great.
Also I know how to make an office crossbow, which could be useful.