The sentence I didn’t write shit today is ambiguous: the idiomatic meaning typically says you didn’t write (or at best, you wrote essentially nothing); the literal meaning typically says that you did write, and what you wrote could not be described as shit. But, I just noticed today, the two roughly opposed meanings can both be true in the same situation! Consider someone who expects daily output to be between 15 and 20 pages, and today they wrote only a page and a half, though it was of high quality. Then on the idiomatic meaning, they didn’t write shit (because a page and a half counts as approximately nothing). But on the literal meaning, they didn’t write any shit: it was all good stuff, not excrement. Both meanings are true!
See, this is the sort of thing I think about. (Just ask Hai about my extended Sluggy Freelance “caca” joke…)