Someone came once to our department and I got tasked with talking to him. He had a big paper with "gravity=levity" and a bunch of marine diagrams, and claimed he could get free energy from sinking (partially hollow) things to the bottom of the ocean and then taking advantage of their buoyancy to drive something on the way back up. Rather than launch into conservation of energy or expound on gravitational potential, I objected "Err, doesn't it take energy to turn them around?" He answered, "Not more than I am getting out of it." I slunk away and left him to his devices.
