Derives from the French "coucou" (cuckoo), which is normally used for greeting in a friendly yet old-fashioned way. Young people have been re-using it, changing it to "kikoo", which sounds even friendlier, and maybe cuter. Teenagers overuse it on communication devices, like MSN, text messages, message boards or blogs. Over time, it has become a way to detect stupid people or just young people (often the two) among the rest of the normal population. Kikoo is a synonym of being less than 14. And stupid.
Boy : Hi, thanks for adding me on MSN
Girl : Kikoo!
Boy : OK forget it.
Basically a person who actually expresses him/herself with word coming from the internet, such as "kikoo" (probably the French "yellow"), lol and so on. They also tend to be teenagers. And very stupid. They will use smileys whenever they can, for no particular reason. They seem to be overenthusiastic about everything. They are annoying and they reproduce. You can find such people in high schools and Skyblogs.
Boy : Nice to meet you I'm Pete
Girl : LOL, I'm Grace.
Boy : OK, never mind. DO NOT WANT Kikoolol