Sitting On The Chair Laughing, a more accurate online abbreviation for internet use, because nobody in their right mind would be "rolling on the floor laughing," or "laughing their ass off." Sitting On the chair Laughing is what they are actually doing. Anybody who types ROFL should perhaps seek help.
SOCL= Sitting on chair laughing. Invented by ehs5 under a msn-conversation because he thought that ROFL is so exaggerated. I'm pretty sure you don't actually are rolling on the floor and laughing when you write ROFL, if you laugh at all, you are sitting on a chair.
ehs5 invented the expression SOCL early 2005, since then it has been used by one other person so it became a little more famous.