Acrylic paint comes off of skin really easy. It kind of itches, though.
I'm going to have to find skin putty for mine. I really don't want to shave half of my eyebrows off. Thanks to 2007 Gaara for that tip!
As a progression update, I got the Medicine Seller's necklace mostly done, his mirror prepped for stenciling, and his obi just a little more painted. The obi is taking a really long time.