Were I you with those kinds of problems I'd think up 2-3 sharp/"sarcastic" replies to interrupt the person answering for you; things like, "Thank you ______ for your answer to the question that was asked me; now if you wouldn't mind, I'd like to give my answer." Especially if it is the same person making the same social mistake. But if it is the same person, maybe I'd start by "warning" them, pointing out to them that I was asked the question and would appreciate it if they'd let me answer. Some people haven't learned the "rules" for some social interactions and have to be "trained". My T use to help me sometimes by doing that, cutting in to let me know when I was out of line. It seems cruel but it doesn't have to be, can be educational and help the person in all their interactions.