Possible spoilers if you want to find out some extra dragon fun for yourself.
Had a dragon decide to pay a visit to my fort. My military dispatched it with no casualties (to start), and besides a major forest fire, all was safe.
...Until random dwarves started bleeding to death. Specifically, military dwarves. At first my friend and I thought it was some kind of strange disease attached to dragons, since the strange part is, it always affected the feet of my dwarves. A few dwarves were lucky and somehow survived with missing right foot fat, but the few I saw before they bled out were bleeding profusely out of every part of one of their feet.
I finally found the cause after inspecting the gear of the last casualty. His boot was covered with dragon blood, and indeed, several other boots were covered with it as well. At first I thought it might've just been some twisted offshoot of the melting fat bug that evaded a swatting, but after looking into the raws, it may be a feature.
Turns out dragon homeotherm is hot. Very hot, in fact, several hundred degrees over the melting point of fat, and still two hundred degrees over the heatdam point of pretty much any organic material.
That means fat will melt quite quickly, and if the poor clueless dwarf doesn't take his boot off fast enough, his skin will eventually boil open and he'll bleed to death... quite a horrifying death. Clothes won't protect a dwarf for long, assuming they've got shoes under those boots. DISREGARD. As stated a couple posts below, most likely cause is the blood being superheated when the dragon breathes flame, then bleeding all over your dwarves' gear. Nonetheless, still a fun feature, and pretty hard to reproduce.
I had a few lucky bastards apparently know what was happening to them. Their right feet are missing fat, but otherwise they're completely fine. The boots are now forbidden, and I'll be seeing if it's possible to wash those boots with water. Or magma, if it comes to it.
Theoretically, this may affect ANY part of metal armor, but boots seem to be the most prone to collect blood. Fortunately, weapons covered with the dragon blood have no effect on the dwarf... but perhaps I should see if it has any effect on enemies.