[ He's literally drawing on the ground, nothing is off limits. ]

Hm.

[ Oh. Finally he will be free of his chalk 'tache. Give him a moment to try and get as much of that chalk off his face without sneezing... ]

I'd like to. There are some clever things you can do with paint on skin - incorporate shape of the body into your work so it flows effortlessly. Play with optical illusions on the skin itself.

But a you have to account for involuntary movement, and if your subject is ticklish, and how that could ruin the art if you aren't careful.