Of course you're right about 'since' and the King's English; "Due to my (state of) not playing Facebook...", "not ever having played Facebook...", or "Having never played Facebook...", while correct, sounded too formal(!) to EFFECTIVELY hide the full-tilt condescension of the reference (although the last one's not so bad). I almost used 'as', but 'since' just sounded (read) more conversational in the context of my reply to Edwin. The formal structure may find its uses, as well: "Having never played Facebook, I shan't deign to opine...."