Means I understand andor agree with what you are saying
Boy A: "What you up to tonight?"
Boy B: "PlayStation"
Boy A: "Skeen"
Pointlessly varied acknowledgements make the Yoofspeak world go round - "safe", "innit", "truth" - a plethora of endlessly flexible retorts that can have differing degrees of meaning for whatever the context demands. Say what you want about the youth of today, but they're demanding with their constant need for approval. "Skeen" is another variation, a word that basically means "I see" or "understood", and is thought to derive from a simple spelling error when the word "seen" was misspelled as "scene", and then mutated. Maybe the offender should have spent less time being emotionally high maintenance and more time doing their English homework.