The inability to adhere to a healthy diet in the face of food seems like the immediately worst one, since it seems liable to cause me to die early.
Presumably there are many others, but being blind spots, they're hard to think of. No doubt I'll go "Oh yes, that's me too" to a lot of the other comments.
How sure are you that you know what healthy food is?
This being said, I find that my appetite is much better regulated if I eat little or no sugar. I think this is fairly common.
It has been noticed since the time immemorial that cognitive biases have a nasty tendency of being invisible to self (note the proverbial log in one's eye). Uncovering their own blind spot is probably the hardest task for an aspired rationalist. EY and others have devoted a number of posts to this issue (e.g. the How To Actually Change Your Mind sequence), and I am wondering if it is bearing fruit for the LW participants.
To this end, I suggest that people post what they think their current rationality blind spot they are struggling with is (not the usual sweet success stories of "overcoming bias"), and let others comment on whether they agree or not, given their impressions of the person here and possibly in real life. My guess is that most of us would miss the mark widely (it's called a blind spot for a reason). Needless to say, if you post, you should expect to get crockered. Also needless to say, if you disagree with a person pointing out your bias, odds are that you are the one who is wrong.
(Who, me, go first? Oh, I have no biases, at least none that I can see.)