Damn im late but this is pretty funny ahahaha.
"Hey (girlfriends name) can you pull your pants down and put on your bikini so I can show a lego forum?"
He wouldn't have needed to say what he wanted the picture for.
Though if I was going to ask for it I'd also ask them to hold up a sign with timestamp, because without it it's just a picture that proves nothing, then again, the sign would make it a rather odd request.