In Vaes Dothrak, Daenerys eats a horse's heart to show how strong her son is going to be. Hmm.
The wise old women of the Dothraki (the dosh khaleen) say that Daenerys will bear the "stallion that will mount the world," the leader who will join all Dothraki together and conquer the world.
At a feast to celebrate, Viserys comes in and threatens his sister with a sword. Khal Drogo promised him a crown of gold and he never got it: boo-hoo is basically his point.
Now, there are several problems with that, including the fact that, in the Dothraki holy city of Vaes Dothrak, no one is supposed to shed blood. (So the sword that Viserys is waving around = big trouble.)
So Khal Drogo gives Viserys his crown of gold: he melts down some of his gold jewelry (he's got a lot of it) and pours it over Viserys' head. That prevents any blood from being spilled and has some poetic justice. Win-win.