Revenge is a dish best served cold

[Donald Trump]

Historians are not sure where the saying originated, but it means that revenge is best served not fresh after the insult occurred, but after enough time has passed so that the target wont see it coming.

[PussyCat]

Old saying from the Mafiosi in Sicily. Tells that the best payback is the one that comes with planning, and that brings the most horrendous pain to your enemies when they are not expecting and are just enjoying the fruits of all the dishonor they brought upon you. One must wait so he can really inflict pain to those who wronged him. Careful planing is necessary so your enemies will suffer terribly, but you wont be harmed by the Law or by your enemies allies.

[Sarah]

A timeless Pashtun proverb. Although frequently claimed by Spanish, French and British imperialists, the proverb is as French as the Egyptian Obelisk in Place de la Concorde Paris. Synonymous with Pashtun culture and a definitive illustration of Pashtunwali or the Pashtun code of conduct. Revenge is a part of life for the Afghan people.
The proverb states that revenge is best served with a clear mind, not when you are hot with anger.

[Mark Zuckerberg]

An old, widely used [phrase] expressing the [sentiment] that [revenge] that is [delayed], and [executed] well after the heat of anger has [dissipated], is more [satisfying] than revenge taken as an immediate act of [rage].
It has been frequently been [claimed] on the Internet to have originated in the [novel] [Les Liaisons Dangereuses] by [Pierre Choderlos de Laclos]. In truth, however, there are two problems with the widely circulated quotation from that book. The first is that the phrase does not appear in the novel, or anything else that de Lacois wrote. The second problem is that the [French] [quotation] used as proof is [linguistically] [erroneous]; de Lacois would never have written the words [attributed] to him. Thus it bears all the [hallmarks] of an Internet fact for which someone [invented] an [authentication] that seemed [plausible], knowing that it would rarely be [verified].
The phrase has been in use since at least the [19th century], and at least one authors use of it back then expressed to the reader that it was an already existing [dictum].
Of course, how long ago it came into being in the [Klingon Empire] would be an interesting subject for [xenolinguistic] [research].

[Couch Potatoe]

A common supervillain saying in soliloquies, meaning that reprisals against enemies, such as superheroes, should be delayed long after the original offense, until the enemies have forgotten them and relaxed security, not expecting an attack. Its origin is unknown, but has been quoted in movies such as Star Trek: The Wrath of Khan, novels such as Mario Puzos The Godfather, etc.

[Britney]

First said by Pierre Ambroise Francois Choderios de LaClos (1741-1803). He originally said it in French in his 1782 book Les Liasons Dangereuses: La vengeance est un plat qui se mange froid. Quoted in Kill Bill Vol. 1 as being an old Klingon Proverb