Thousands of years of war have hard-wired respect for Dragon Slayers into the Yarge psyche. The invention of firearms didn’t change that, but for the most part it’s considered dishonourable to claim the title if all you have done is pull a trigger. While there are no official rules, at least that anyone will admit to, most Yarge only accord full respect to someone who single-handedly fulfils all of the following criteria:
1. Killed a healthy active adult dragon
2. Without using firearms
3. In the presence of witnesses
4. For good reason
5. At risk to their own life and
The first criterion rules out anyone who kills a hatchling, a dragon already on the verge of death, or one that is caged or incapacitated in some way, for example by being drunk or drugged.
The second doesn’t necessarily apply just to firearms; any “unfair” method (such as running down a dragon with a steam car) is similarly frowned on.
The third is just common sense – how can anyone know that you’re a dragon slayer if nobody saw it happen? Witnesses are needed, preferably unbiased ones.
The fourth should be obvious; the Yarge don’t want to provoke dragons unnecessarily. There must be a good reason to kill the dragon, without one there is a good chance of being considered a murderer. Staged dragon hunts of any kind are not considered good reason.
The fifth is also obvious; without risk, killing a dragon is mere butchery.
As for the sixth, the title is occasionally awarded posthumously, for an especially noteworthy feat – for example, stabbing a dragon through the roof of its mouth as it bites off your hand – but for the most part death by dragon is considered a form of suicide.
Except in time of war there are rarely more than one or two living dragon slayers. Currently the only claimants are the Sultan of Rasdogah Erofal (unverified) and Keleg of the Yegith Archipelago (verified but reasons open to question).
I should add that this hasn't yet been approved by papersky, though I hope it will be.