Don't get mad, get even there is more satisfaction in requiting a wrong than resenting it. Proverbial saying, late 20th century (compare the earlier revenge is a dish that can be eaten cold).
mad as a hatter completely insane. Hat-makers sometimes suffered from mercury poisoning as a result of the use of mercurous nitrate in the manufacture of felt hats, and the idea was personified in one of the two eccentric hosts (the Mad Hatter) at the ‘mad tea party’ in Lewis Carroll's Alice's Adventures in Wonderland (1865).
mad as a March hare completely insane; the allusion here is to the running and leaping of hares in the breeding season, and again was reinforced by the character created by Lewis Carroll in Alice's Adventures in Wonderland (1865).
See also whom the gods would destroy, they first make mad.