If by "rationalist", the LW community means someone who believes it is possible and desirable to make at least the most important judgements solely by the use of reason operating on empirically demonstrable facts, then I am an ex-rationalist. My "intellectual stew" had simmered into it several forms of formal logic, applied math, and seasoned with a BS in Computer Science at age 23.
By age 28 or so, I concluded that most of the really important things in life were not amenable to this approach, and that the type of thinking I had learned was useful for earning a living, but was woefully inadequate for other purposes.
At age 50, I am still refining the way I think. I come to LW to lurk, learn, and (occasionally) quibble.
Welcome to Less Wrong!
You might want to post your introduction in the current official "welcome" thread.
... then I am an ex-rationalist.
LW's notion of rationality differs greatly from what you described. You may find our version more palatable.
To break up the awkward silence at the start of a recent Overcoming Bias meetup, I asked everyone present to tell their rationalist origin story - a key event or fact that played a role in their first beginning to aspire to rationality. This worked surprisingly well (and I would recommend it for future meetups).
I think I've already told enough of my own origin story on Overcoming Bias: how I was digging in my parents' yard as a kid and found a tarnished silver amulet inscribed with Bayes's Theorem, and how I wore it to bed that night and dreamed of a woman in white, holding an ancient leather-bound book called Judgment Under Uncertainty: Heuristics and Biases (eds. D. Kahneman, P. Slovic, and A. Tversky, 1982)... but there's no need to go into that again.
So, seriously... how did you originally go down that road?
Added: For some odd reason, many of the commenters here seem to have had a single experience in common - namely, at some point, encountering Overcoming Bias... But I'm especially interested in what it takes to get the transition started - crossing the first divide. This would be very valuable knowledge if it can be generalized. If that did happen at OB, please try to specify what was the crucial "Aha!" insight (down to the specific post if possible).