Similar to 'pwned' or 'pwnd' in that it is a shortened form of an already out-of-context term used to insult others, typically on internet-based forums or games.
H4L0WH0R3: lol skld
G1ZM31STER: skld? wtf
H4L0WH0R3: it's like pwnd. I'm trying to bring it in. Go with it.
G1ZM31STER: O. OK. SKLD!!1!!!111