He thinks all the dead skin and sweat from all the astronauts over all the years would have accumulated to make the ISS into a smelly, disgusting tin-can.
He sends me websites where some nut has analysed the speed of Saturn V shadows against clouds as it lifts off to prove that it never achieved orbital velocity so it never made it to space. Also that the F1 engines never had enough power to lift a real, fully fuelled 3rd stage, command module and lander. He also sends me fruitcake analysis of moon photos 'proving' they were faked.