>"I'm well aware of how HIV leads to AIDS. . . "
Then use the right term. If someone who reads things in context and considers who's saying what had made such a stupid little mix-up like confounding HIV for AIDS, I'd let it pass. But you're the one policing volcabulary and projecting all sorts of beliefs and ideas onto others.
>"treating an individual differently because he belongs to a certain social demographic is prejudice." Of course it is. But does it help or hurt? If I chase after a Celt with SPF50 lotion more quickly than I do for a southern Euporean, I'm making all sorts of assumptions. Similary, I attach no stigma to the HIV+ person, but (if I was the medical provider) would want to be able to respond with appropriate care and some medical conditions make a big difference in patient care.
"twink", like "bear" is, in my circles, simply descriptive. Not pegorative. If I'm in a dialouge with Dan Savage, he's pulling all sorts of terms (and their meanings) from the dominant culture. As I am with terms from different subcultures including many to which I don't belong. I know there are highly dramatic and extended debates about whether a non-member of a (gay, black, kink, vor, etc) community should use vocab from that community. The n-word (youtube Tim Minchin on that) for blacks and the d-word for lesbians are, in my opinion, still too dodgy to use more widely. But on a daily basis, I usurp terms from Spanish (Sierra) Hispanic (burrito), French (ala mode), Black (rock&roll), gay, geek, Star Trek, and academic cultures. And I'm not going to stop. To each their own.
Much of this reminds of "janitors" becoming "custodians" 40 years ago. I never saw the problem as they were doing important, neccessary work and I didn't look down on them. But for people who saw the janitors as "the lowly guys who hauls the trash", the new terms quickly had all the same negative connotations.
Reread what I wrote in the context of "an ally who doesn't police his vocabulary and was giving an extreme example of not disclosing health issues to make a point." and maybe it wouldn't seem so evil.