From
community.livejournal.com/ask_an_aspie/11381.html ...
My guess would be that wood and metal are a metaphor for "intransigent".
I'm only beginning to recognize a few of my states of mind as being rare for non-autistics. One of them is when I know that it will take me 3hrs to go to the store because I'm going to get lost in it. Another is the rush and near panic I sometimes feel while packing for a trip - I need to take a lot of time, make lists, etc. If I haven't done that, I often forget something important which distresses me greatly. I get a similar "overhurried" feeling just before some social events that I'm feeling so-so about attending. I feel like I have this other thing that I need to do first... but if I give in to that, then I'm either dreadfully and antisocially late, or I end up standing people up without notice, neither of which is socially acceptable.
None of those necessarily constitutes a "bad day", though, from anyone else's perspective. The worst case in those is that I appear to behave slightly erratically or flakily from their perspective. The closest I get to a "bad day" are periods when I'm not open to change, and yet change appears to be happening to and around me without my participation. In those times I can become extremely angry, exasperated, frustrated, bull headed, emphatic, and... unbending. At these times I can certainly appear argumentative.
So my guess is that "wood and metal" might refer to the experience of being unbending or resolute.