1. Variation on the phrase "Okay, Okay, Thanks... Later".
Etymology: Originated in the Online MMORPG (EverQuest) scene, and a hybridization of kkthxbye. Commonly used on forums, and in-game. Where it's usage was first seen is debatable.
Person 1: "I've got your J-boots quest bagged man, so I'll see you tomorrow."
Person 2: "kkthxla~"