There's an episode in which he takes a celebrity with him on a survivor mission. He travelled with Will Ferrell to Sweden and they were going to go to the north of the country and show how to survive in extreme cold. As soon as their plane touched down in Stockholm and they were walking through the airport, Ferrell was asking "Is this where we drink our own urine?" .
Thought that was very funny.
Most disgusting thing I've seen Grylls do is pick up an elephant turd, hold it over his head, mouth wide open, and squeeze the liquid out.