"Revenge is a dish best served cold."
It means that revenge is more satisfying when one has had time to prepare vengeance that is well-planned, long-feared, or unexpected.
Let's say you lose out on a promotion because your rival spread lies about you and exaggerated his own skills. You just smile, do as you're told, and stay out of trouble. No one knows you are plotting revenge.
10 years later, the police arrest your rival in his office. It seems they received an anonymous tip regarding your rival's illegal business dealings, along with enough evidence to press charges. His arrest leads to the termination of his employment. You respond to all of this with shock and dismay.
These events also require that you be promoted to his (now former) position. You then proceed to quietly remove his name from every on-line file relating to successful projects. Eventually, all the record show only that he once worked there, but did very little to justify his employment.
THAT, young padawan, is an example of "Cold Revenge".
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No love for Hamas, Hezbollah, Iranian Leadership, Islamic Jihad, other Islamic terrorist groups, OR their supporters and sympathizers.