I like to RP my Sith as a really, really
slow Sith, like Forrest Gump/Fezzik style, and watch the lulz come right out. Although I don't RP as much anymore since the friends i used to RP with have taken breaks for differing reasons (they're still subbed), my SIth is pretty much unaware he's a Sith most of the time.
In fact, my Sith is generally unaware of his name until my friend's character reminds him of it. It is absolutely so much fun playing him, he's just fantastic.
(Yes, i have an actual explanation for this in-game.