KTK is shorthand for the Maori statement of 'Kei te kata', or I am laughing, same as LOL

"Kill The Keg". Refers to the consumption of the remainder of a keg of beer. Killing the keg is most commonly done in fraternities; the pledge class is told to "kill the keg" in a certain amount of time.

KTK is a versatile word that may be used in any context. The first "k" stands for "kook", a version of the word "cook" (both pronounced the same way). It acts as the verb. "T" stands simply for "the" and the last "k" stands for "kut" (pronounced the same way as "cut"). The "kut" is the most important part of the entire phrase as it can be used as an verb, adjective, noun, adverb, etc. The "kut" was originally a road in the Northern California East Bay by a team called the Rising Suns.

So, in it's entirety, it is "Kook the KUT!".

For example: When you play CS:GO and you kill someone, and another person kills you at the same time too.
Chat:
User1: Haha!
User2: ktk
ktk - Kill The Killer