I saw a guy do it once at the range, but he was mainly just showing off. The position is well described in [1], which may be of interest to you if you're not solely poking at the grandparent commenter's having confused 'supine' with 'prone'.
> if you're not solely poking at the grandparent commenter's having confused 'supine' with 'prone'
In my experience, people commonly use "lie prone" to mean basically any position, but nobody knows the word "supine" except in its technical meaning contrasting with "prone". Thus, I thought this was worth clarifying; I'd be happy to assume that someone using "prone" in a context that heavily suggested another position just didn't think of "prone" as referring to any position in particular; that seemed like an odd assumption for "supine".
Do you have a suggestion for wording the question so as not to sound insulting?
I'm not sure I do; I read it as smart-alecky because that's what it would have been had I written it, but on reflection I don't suppose you meant it that way, and I didn't intend to suggest in my response that I thought yours insulting.
I suppose I did come off a bit unduly bitchy, though, and I'm sorry for that. Some weeks go by in a moment; others feel like they drag on for months. This last was one of the latter sort, but there was no call for me to go and take that out on you.
[1] http://firearmshistory.blogspot.com/2012/03/rifle-shooting-p...