Plan one or two short lines you can use on repeat so you do not have to think in the moment. Start light but firm so you do not create drama. Try a calm call-in like, Oof, that landed harsh. Let's keep it kind. Or use the confused face and ask, I'm not following. What do you mean by that. Both force them to own the joke without you attacking. If it continues, name the boundary plainly: Please do not joke about me like that. I am here to have a good time. If they push again, use the broken record and consequence: I am not OK with that. I will step away if it keeps up. Then actually disengage for a few minutes.
Before the next group hang, give your partner a heads-up and a simple role. Ask them to back you by redirecting immediately, like, Hey, knock it off, or by changing the subject. You can even set a subtle signal so they know when to jump in. In the moment, keep your tone steady, volume normal, and smile small so it reads as boundary not fight. If the group laughs, hold your line and then pivot the topic yourself to defuse. Afterward, tell your partner what worked and what did not so you two stay aligned. Consistency is key, and most people stop when they learn you will not play along.
