Was invited to repost this here. Seven in Mrs Dragon's tight ass. We had actually gone out and bought two packs of twelve just for this challenge, but that was apparently a little over optimistic. Still, not bad for a first try.
Apparently the human anus can stretch up to 5 inches in diameter (2.5 inches radius). A sharpie marker is roughly 11mm in diameter (.433 inches). Math shows weβre a long way from the max record!