"Oh, sorry, I didn't realize it was time for today's crack about Jones and me. Do go on."
"*Sigh* You children are so easily amused. How long will it be before you're bored with these jokes? 'Cause, seriously, they should be mummified by now."
"Gosh, that's funny! And so original! Lay another one on me!"
"Yeah, I was just talking to Jones about that. Yes, Jones. We might be secretly shtupping, yada, yada. Anyway . . ."
IMHO, in these environments, it's best to turn the cracks right back at the perpetrators. Hang a lampshade on how old the jokes are getting. The people making them will draw less shame from making you feel uncomfortable than they will from being exposed as unfunny.