If someone says don't get mad, get even, they mean that if someone harms you, you should not waste your energy on being angry, but concentrate on harming them in return. Relationships here seem to work on a don't get mad, get even principle. So if I'm late by ten minutes for an appointment to meet you, the next time we meet you are late by the same number of minutes, and so on. Note: This expression is believed to have come from the strong-willed Irish-American politician Joseph P Kennedy, father of John F Kennedy. A book by Alan Abel with this title, described as `a manual for retaliation', was published in 1983.

COMMON If you get even with someone who has hurt or insulted you, you get your revenge on them. He is so furious about their treatment of him that he's determined to get even. He'd leapt at this chance to get even with the guy who had taken his money.