1-Revenge is a dish that is best served cold
Which is not really a Klingon proverb, but is from various Earth sources, notably Les Liaisons Dangereuses
. I've never taken Khan's line about it too seriously -- after all, when did he get the chance to learn anything about Klingons?
On the Enterprise before Kirk banished him?
In my novelization of "The Best of Both Worlds," I gave Worf a line, "Kahless himself said that a clear mind is the greatest ally a warrior has."