Young Sheldon, Season 1 Episode 11 "I was once visited by nine"
The entire quote, after young Sheldon is awakened from his binary meaning to the universe dream, Jim Parsons speaks the words:
"I was once visited by Nine when I had chickenpox. He was a lot less funny than he thought he was."
I think "visited by Nine" and "a lot less funny" probably references something because it's so specific, but I have no idea what that's referencing and neither Google nor Urban Dictionary was any help.
In the episode Sheldon is visited by two characters - One and Zero - who claim to be "the binary code underlying everything" and are about to tell Sheldon the Secret of the Universe, before they are disturbed. We can reasonably conclude that they are products of Sheldon's imagination and/or hallucinatory dreams.
Sheldon says that he never hears from them again, but does encounter "Nine", who we can assume from his name is a similar dreamed character, especially since he arrives when Sheldon is sick with chickenpox, a time when children tend to have unusual dreams.