It’s one thing to say “do a Shakespeare theme” for Halloween (for grownups), but if you think about it, it’s quite the commitment. Most people can bust out some form of athlete / construction worker / medical personnel based entirely on stuff already in their closet or easily borrowed. But try doing Beatrice and Benedick without having some friends who are either directly involved in the theatre (and hence may have some stuff), or else are crazy into the Renaissance Festival scene. Either way you’re going to spend the night explaining to people who you are, anyway :).
UPDATED: More Shakespeare Halloween Ideas!