Abbreviation for the Japanese expression "kita kore" (来たこれ), lit. "it has come", "it came!"
Usually expressed after a certain event or occurrence which satisfied a certain expectation of the viewer/commenter.
Commonly used on Japanese sites like the 2ch boards and Nico Nico Douga for instance.
Often seen in conjunction with wktk.
Case 1: Random video on Niconico where a random embarrassing/funny scene has been shown. Result: hundreds of on-screen comments go "ＫＴＫＲ" "ｋｔｋｒ ちょｗｗｗｗｗｗ" "ｋｉｔａ ｋｏｒｅ ｗｗｗ".
Case 2: Random boy gets a random anime figurine, logs onto his random blog/facebook/twitter and goes "finally got my 100th fig ktkr!!!!1 Here's for 200 wktk!"