Why is "the" used here? I would use not article in this dialog
It upsets Sheldon when you play with the food...It upsets Sheldon when you play with the Sheldon. First sentence I kinda can justify the, second one - just don't get it.
(The big bang theory. https://www.youtube.com/watch?v=mCK6ZwpNICQ)
It's just a jokey continuation of the conversation. Prior to this there are several instances where they say, "It upsets Sheldon when you play with the X."
It also jokingly insinuates that there is only one 'Sheldon' in the world and at the same time dehumanises him somewhat.