considering that yaoi comprise of boyxboy,
and that they usually end up having anal sex,
and that sexually transmitted diease are as likely passable in anal sex as any other sex,
and that their sex doesn't serve any reproductive functions,
none of them ever use protection

can anybody show me a yaoi that actually uses protection in their sex?

Rumble Rush (and some of the other titles by the mangaka I think)
Sono Kuchibiru ni Yoru no Tsuyu

I'm pretty sure there are more... Few, but there are more. ;3

Oh, there's UGH as well and in other titles she writes
(read some more recently ;p).

Hrodulf and Bjornolfr, you will not be forgotten.
[img]http://i411.photobucket.com/albums/pp199/SyberAngelGabrielle/couplesig.jpg[/img]
[color=black]And if the world were black and white,
you would be my rainbow in shades of grey.[/color]

Click 'n Play!

If I had a fantasy self, it'd be a tentacle monster.

I can't name any since I don't remember minor details like that, but I think it's more common than you think. I'm pretty sure a good majority of yaoi has protection, though it doesn't make a big deal/scene about it. Just little notions like "did you put on a condom," seeing condoms on the floor, etc.

edit/
Yatteraneeze! deals with protection and what happens if you don't use it.

There's definitely a condom in Yellow. Made me rather happy to see, actually.

Breath.

Surf Junkie - It' just a passing notion though, but it's good to know they're practicing safe sex.

😀 reminds me of a hentai manga i read once about a boy who enters a store because his older sibling tells him to buy condoms - he doesnt know what they are the store clerk gets aroused and she ends up seducing him, and after having sex she realizes she forgot to use a condom