Via the BB Submitterator, Melanie says,
A camera crew for the show Into the Drink was filming Mantas off the coast of Kailua-Kona, Hawaii when one of the giant Pacific Manta Rays took a camera off one of the divers. After swimming around for a bit with the camera still rolling, the Manta dropped the rig off on the sea floor under their boat. Another diver filmed the camera equipment being taken by the Manta.
Video and more about the manta mugging here (grindtv.com).