To me, this does not sound like your trying to go for what is considered a witty personality. That sounds like someone who takes sarcasm to an extreme thats downright mean. BUT once again, I will refer to one of my favorite authors for this. There is a character in David Edding's books named Silk. He is both clever and witty and extremely intelligent, humorous and sarcastic, cruel sometimes, AND has a women that is his equal, who manages to shove humility down his throat in every interaction. (He eventually marries her.) SO it also shows a developing romance between the two characters.
I find that wit and humour are the most difficult things to fake as a writer, and I would never have the guts to attempt to write a wonderfully witty character, whatever that means. But still, a lot of my characters, even bad ones, end up with funny lines, and are considered quite witty, even though there is not much effort on my part. If it naturally comes to me, a really good comeback, then I'm delighted. But to write a character who always has a great comeback line, you have to be that kind of person too. And I am one of those people who stays up at night obsessing about a humiliating conversation earlier in the day, and only then, at 2 am, I think of a perfect comeback. In any case, just make sure when you try to write "witty" you don't write "obnoxious" because that's how all my failed attempts end up sounding. Brrr...
Excellent example. Tyrion is a great source for self-deprecating humor or just firing back at someone who insults him, and since he's almost always being insulted, the books are full of great Tyrion lines. Also, the character Dolorous Edd is there just for comedic relief. His lines (though fewer) are always funny. For hateful jokes, the character Cercei Lannister is a good source.