I assumed the HN crowd was familiar with the fact that "90% of everything is crap" is someone else's idea. This was probably not a good assumption to make.
Even if they are, framing matters. Your framing sounded like "this is my (ugly) opinion" not like "Everyone knows this common saying."
I don't know why people are giving you a hard time here. The quote is widely-known, and I appreciated your remark about the troubling lack of falsifiability criterion.
See elsewhere here, there's no shortage of experiments to be done that could be determinative in this case. Also, Karl Popper's rule is a great rule of thumb, it really is; but there's an immense bibliography in philosophy of science about whether it's a shoe that fits all circumstances.
So familiar, so why state it without any special relevance, much less without attribution? Why waste our time then if everybody knows it?