I think if you write a code that the computer interprets and does something with that code, that is by any definition "coding". I know there's often a "code" vs. "design" distinction, but HTML/CSS are by their very definition codes.

HTML/CSS are markup languages, not programming languages. One is a way of defining what something is, the other is a way of defining what something does. Think Markdown vs. Python, for a more dramatic example.

I understand that, but they're written with code. Maybe I'm wrong but that pretty clearly makes the writing of them "coding".

You're taking a word too literally and conflating it with something it doesn't mean.

HTML/CSS is not coding/programming.

I'm amenable to that argument, I can't find an alternate definition that disputes my use of the word and there are dozens of uses of the word "coding" to mean writing html/css, so I don't know what alternate definition I'm supposed to be using.

Popular use doesn't define reality.

omg HN people always the same argument with you. HTML/CSS is coding and if you want me to take it an extra step and call it CSS programming I will, because it turns out it's turing complete. BOOM! http://jsfiddle.net/Camilo/eQyBa/