Here are two more takes on the Cheshire Cat design idea: one with whiskers, and the other without. Not sure which would be best – while the first looks more like the face of the Cat, the second is cleaner looking as a design.
Val Resh suggested use of Edward Munch’s “The Scream”, which has long been associated with madness. (I know that Mad Pridester Dolly Sen has dressed as The Scream during one of her performances, for example: http://www.dollysen.com/collaborate.htm
More to come!