LOL! One time a co-worker sent a prank e-mail saying he was being sent on an assignment out of state for a couple months so we should all buy him lunch. I was able to spoof an e-mail reply "from our director" who was very angry that the finance office had pulled him out of an important meeting because they didn't know what travel plans to make for this guy and that he'd better have a good explanation for all of this or he might as well start packing up his personal belongings.

I watched him open and read the e-mail and the "oh crap" look on his face was priceless. I caught him just before he was going to run into the director's office and beg for his job.