I've seen a couple blogs out there that did something like this, but they just free handed the design. I don't have that much faith in my drawing skills . . . plus, I wanted both sides of the mustache to be the same - like mirror images and I knew I would mess it up if I just painted on the mug without a stencil of sorts.
I used porcelain paint that I found at Michael's and a non-foam paint brush. The rest is pretty self explanatory.