I had a last generation blue Black Diamond Half Dome climbing helmet (they suck so bad, NEVER get one of the old ones, they don't fit heads right), which is like the most common color/model ever. I used spray paint and stickers as stencils. I put three coats of spray on poly-u as a protectant, too. Personally I think that OP's friend's helmet looks cool as is. I definitely wouldn't put a solid coat on. You might experiment with some multi-colored splatters or a couple asymmetrical stripes.
Pretty funny story how that little saying came to be. Ask me on the lift some time.
I'm a happy camper.
Let's put a GoPro on Tourettes Guy.