Symbolism, Imagery, Allegory
Characters are always accusing others of being crazy. "You're a lunatic!" "No, you're a nutcase!" and so forth. Madness or insanity is mostly code for wacky, silly, or zany, which is exactly how one can describe the hard partying of Toby and Aguecheek, the elaborate prank Maria devises to punish Malvolio, and the various misguided pursuits of love in Twelfth Night. We discuss this in more detail under "Foolishness and Folly," so be sure to check that out.