There's a couple of banging bandits on the loose in Vegas -- after they got busted celebrating "Fifty Shades of Grey" all over a Sin City museum ... which may seem appropriate, but it's still illegal.
TMZ obtained surveillance video of their bare-assed exploits around the Erotic Heritage Museum -- which was featuring an homage to kink on Valentine's Day ... and after-hours the couple went on a room-by-room sex spree.
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