Was the Golden Crown given to anyone else before?

May contain cynicism^[1]…

I'm not sure what could give you the idea that it would be a long-standing tradition to melt down everybody's jewellery to present a crown [at any temperature] to any passing claimant who's been promised one in exchange for his sister & keeps on nagging about it like a 12-year-old promised a weekend at DisneyLand.

I think it's fairly safe to say this particular punishment was thought up on the spot.

Think of it as the Dothraki equivalent of being shot in the head for saying "Are we there yet?" once too often. They are never portrayed as being particularly patient or tolerant.

I would consider the prior discussion as one of method rather than end result. The crown would amuse the Dothraki [and shock the audience] as being a fitting punishment, far more than just chopping his head off.

^[1]_{Similar to the warning, "May contain nuts". Doesn't bother most people, though some may find it detrimental;)}

No, this was not a traditional punishment.

While it is never stated on the show that pouring molten gold on someone's head was not something the Dothraki had ever done before, there are two facts that strongly weigh against it being a traditional punishment. The first is that it was never described as such in the book. Martin's Song of Ice and Fire books are extremely rich in detail about the various cultures in that fantasy world and had the author intended for this to be some Dothraki tradition, it is near certain that he would have provided that background. The second is that Ser Jorah was there to advise Vyserys, he seemed to be quite well versed in Dothraki culture, and he did not say anything about it to Vyserys. Had this been something that the Dothraki were known to do, Jorah likely would have warned Vyserys about it the minute Khal Drago promised him a "crown of gold." He would have used the knowledge to rein in Vyserys's impatience and impudence long before it got to the point where Drago had had enough.