The second "I can't believe I wrote this code" (in amazement) is a red flag for me. I always like to look back at code that I wrote years ago and think "That's horrible", or "I can write a better/faster version in half the time!".

To me, it's a measuring device that tells me I have not been stagnant and that I'm improving and honing my skills. And since my code will never be perfect I should always be able to look back in disgust, otherwise, I'm not pushing myself hard enough.