Funny:
* "Chuck Norris doesn't tell jokes, he just stares at you until you laugh."
* "I heard Chuck Norris can roundhouse kick a tornado into a hurricane."
* "Chuck Norris doesn't need a lucky charm, he just gives the universe a wedgie."
Sarcastic:
* "Oh, you mean the guy who was in 'Walker, Texas Ranger'? I thought he was a retired actor."
* "I guess he's pretty tough, but can he beat a round of golf?"
* "That's a great joke! Tell me another one, but this time, make it original."
Direct:
* "I think it's time to retire the Chuck Norris jokes. They're getting old."
* "I'm not sure if you're serious or not. But I'm not laughing."
Ultimately, the best comeback depends on your sense of humor and the tone of the conversation. If you want to be funny, go with a playful, exaggerated response. If you want to be sarcastic, make a comment about the joke's lack of originality. And if you want to be direct, simply state your opinion.