Hawking had an awesome sense of humour. That interview is amazing.
Did Johnny boy know that Stephen Hawking was going to tell him:
You are an idiot
It took Hawking minutes to create some responses. Without the use of his hand due to his disease, he relied on the twitch of a few facial muscles to select from a list of available words.
As funny as it is, that interview, or any interview with Hawkins contains pre-drafted responses from Hawking and follows a script.
But the small facial movements showing his emotion still showed Hawking had fun doing it.