"I knew eating a cookie wasn't good for me, but I felt like it and so I did it anyway."
I'm like this for my trivial decisions but not for major ones. I virtually never rationalise eating choices, the choice is purely a conflict between deciding whether I'm going to do what I want vs what I ought.
I do notice myself rationalising when making more long-term decisions and in arguments - if I'm unsure of a decision I'll sometimes make a list of pros and cons and catch myself trying to rig the outcome (which is an answer in itself, obviously). Or if I get into an argument I sometimes catch myself going into "arguments as soldiers" mode, which feels quite similar to rationalising.
Anyway, my point for both is that for me at least, rationalisation only seems to pop up when the stakes are higher. If you gave me your earlier example about wanting to eat pizza and making excuses about calcium, I'd probably look at you as though you had 3 heads too.
Anna Salamon and I are confused. Both of us notice ourselves rationalizing on pretty much a daily basis and have to apply techniques like the Litany of Tarski pretty regularly. But in several of our test sessions for teaching rationality, a handful of people report never rationalizing and seem to have little clue what Tarski is for. They don't relate to any examples we give, whether fictitious or actual personal examples from our lives. Some of these people show signs of being rather high-level rationalists overall, although some don't.