Thanks for pointing this out; I didn't read all the comments previously (only the first third, or so) because there is so many of them. (Here is a link to the HPMoR comment, for other curious people.) I've read the remaining ones now.

By the way, the comments are closed today. (They were still open yesterday.) I am happy someone was fast enough to post there this:

Somewhat related: a major rationalist perspective on the importance of saying oops (http://lesswrong.com/lw/i9/the_importance_of_saying_oops/) (hint: it’s very important, the guy you’re dealing with should have done it a long time ago for all the things he messed up on, and you should flee him) and feelings (http://lesswrong.com/lw/hp/feeling_rational/) (hint: it is rational to feel, not to deny others’ feelings).

tl;dr: LW, this dude is calling himself “rational” but is not rational.

Reading the comments, I am impressed by their high quality. I actually feared something like using "rationality" as a boo light, but there is only an occassional fallacy of gray (everyone is equally irrational), and only a very few commenters try to generalize the behavior to men in general. Based on my experience from the rest of the internet, I expected much more of that. Actually, there are also some very smart comments, like:

it is rational and logical to take emotions into account. Emotions are real things that human beings have – we have them often for good reasons, and we’re not Vulcans (besides, I’m betting both Spock and Tuvok have really neat clean quarters and would never leave broken glass lying around to defy the man, because it would not be logical). Anyway. Emotions are valid. Caring for the emotional well being of your loved ones is important and also a rational choice. People have different preferences for things, and feel differently about things, and negotiating those differences is a huge part of a good relationship.

If by chance the person who wrote the letter comes here, I strongly recommend reading "The Mask of Sanity" for a descriptions of how psychopaths work. I believe some of the examples would pattern-match very strongly.

And the lesson for the LessWrong community is probably this: Some psychopaths will find LW and HPMoR, and will use "rationality" as their excuse. We should probably have some visible FAQ that contradicts them. (On a second thought: Having the FAQ on LessWrong would not have helped in this specific case, because the abusive boyfriend only showed her HPMoR. And having this kind of disclaimer on HPMoR would probably feel weird. Maybe the best solution would be to have a link to the LessWrong FAQ on the HPMoR web page; something like: "This fan fiction is about rationality. Read here more about what is - and what isn't - considered rational by its author.)