[jules]

I thought that both these meanings of shy were already negative?

Note that in the association is between two meanings of a word: the association is between one meaning of shy and the other, not between shy and the girl. The latter are only associated because you used them together in a sentence. So the fact that you used "We were just shy of our goal" does not associate "girl" with something negative. It does associate "shy" with something negative. In contrast, if you use "that movie is gay", just by using that sentence on its own you are associating "gay", and hence a group of people, with "bad".

For why there is more backlash in one case than another you also have to keep in mind the direct effect. If you say "We were just shy of our goal", the potential to hurt a shy person who happens to listen in will likely not be large, but if you say "that movie is gay" and a gay person is listening in, it might very well hurt. Secondly, shy is already negative, so it would be a little strange to complain that using it as "almost but not quite" is damaging the status of shy people, since the other meaning of shy is already more negative.

[randomdata]

There is nothing inherently negative about being shy by the dictionary definition of the word.

I tend to agree that we have attached negativity to the usage, but only in the the way that gay is used negatively. They are often both used to point out "flaws", for lack of a better term, in other people. (not that either is a real flaw; only in the eye of some beholders)

I find it interesting that you assume that shy is already negative. I was actually skeptical of your original comment at first, but perhaps this actually serves to reenforce it.