After talking to a couple of people about this, I should qualify/partially-retract the original comment.

Some people have suggested to me that the best metaphor a man can use to understand how women think about "nice guys" isn't an ugly duckling woman who gets turned down by the men she likes, but a grossly obese woman who never showers or shaves her legs, and who goes around complaining loudly to everyone she knows that men are all vapid pigs who are only interested in looks.

I would find this person annoying, and although I hope I would be kind enough not to lash out against her in quite the terms I mentioned above, I would understand the motivations of someone who did, instead of having to classify him as having some sort of weird Martian brain design that makes him a moral monster.

The obesity metaphor is especially relevant. Since there are people out there who think becoming skinny is as easy as "just eat less food", I can imagine people who think becoming socially assertive really is as easy as "just talk to people and be more confident".

For people who honestly believe those things, and there seem to be a lot of them, the obese woman and the socially awkward man would reduce to the case of the woman who never showered but constantly complained about how superficial men were to reject her over her smell - annoying and without any redeeming value.