Wit doesn’t get much better than this. Bierce would have liked me to say it does not get any better than his! Here is one definition from the strictly adorable Devil’s Dictionary:
MAD, adj. Affected with a high degree of intellectual independence; not conforming to standards of thought, speech and action derived by the conformants from study of themselves; at odds with the majority; in short, unusual. It is noteworthy that persons are pronounced mad by officials destitute of evidence that themselves are sane. For illustration, this present (and illustrious) lexicographer is no firmer in the faith of his own sanity than is any inmate of any madhouse of the land; yet for aught he knows to the contrary, instead of the lofty occupation that seems to him to be engaging his powers he may really be beating his hands against the window bars of an asylum and declaring himself Noah Webster, to the innocent delights of many thoughtless spectators.