The Sistene chapel was definitely the worst. There was a (reasonably) orderly and (very) long queue to get in, with at least 50 signs along the way in as many languages saying 'DO NOT TAKE PHOTOGRAPHS, it will PERMANENTLY DAMAGE the ceiling'. Then when we got in, it can only be described as pandemonium: the three guards had arrayed themselves into a line and were getting ready to charge a group of gigantic rowdy Americans, everyone was shouting as loudly as possible in their native language, trying to drown out everyone else's language (it was a close call between the Chinese and the Americans as to who was winning) and everyone, and I mean literally EVERYONE (including me, since I figured a drop in the ocean wouldn't make much difference) was flashing their cameras at the ceiling as if they had a personal vendetta against epileptic people, waving them around, and getting in the way of everyone else who was coming into the microscopic-sized room, meanwhile blocking the exit out.
And all of that to see a picture I've seen a million times in other places.