Okay, I have to get my hands on one of these awesome whiteboard shirts! However, I'm guessing it's pretty hard to draw upside down, at least until your brain gets used to it.
Become a master like Phil Hansen, who quickly sketches 38 different portraits of cinematic badasses on his shirt, and you too can have the fame and critical acclaim afforded to those who keep the interwebs entertained. Yay for creativity!