_Clean Code_ is an extremely well-known book on programming by Robert “Uncle Bob” Martin from the 2000s. Posts about it have come up on HN as recently as this year.
Maybe it’s a sign of the times, but I’m surprised you’ve never come across it. I say this as someone who doesn’t agree with many of the suggestions.
The fact that he capitalized both Cs indicates he's talking about the book, which is famous enough that I learned about it and its influence when I was in school ~15 years ago.
GP wrote clean code (lowercase) which most people would take to mean the general practices of hygenic, well maintained code.
When most people think of "clean code", they are not thinking about whatever got you so worked up.