If Khal Drogo was a Sith, he'd probably be known as Darth Drogo. Here's some fan art by jbcasacop on Deviant Art, the first in a new series called Star Wars: The Throne Wars.

Writes jbcasacop:
Dark lord of the Khalasar. I'm a fan of Star Wars. I'm also a fan of Game of Thrones. I couldn't decide which one I was going to make fan art of so I thought of doing both! Here's our favorite Dothraki depicted as a sith. This is the first of my Star Wars: The Throne Wars series. I shall make use of my spare time to make more of these!
He'd probably be more bad ass than Darth Vader. Really. Just look at him.