That IS absolutely hilarious.
And admittedly, it's quite clever. He doesn't really have to do much other than sign in, just stand there and watch the chaos unfold. I don't think he was so much a jerk, as someone trying to see what would happen. This kind of helps Microsoft in the end, in finding areas to improve upon.
If I were them, I'd make any voice commands unable to be used as gamertags. Shouldn't be too hard to protect those as system functions.