That's a reflection of their own impatience, and I doubt they do it only with stutterers. You could be completely fluent, but some people are self-absorbed assholes who can't get over themselves. Their ego doesn't much discriminate between people who stutter and people who are fluent. I tend to double down or even triple down. Odds are they won't listen, but they will stop interrupting until you're done. I find slight satisfaction in that. You're essentially doubling down until they are conditioned into finding the behavior of interrupting unrewarding. Operant conditioning, Pavlov's dog, and all that. 🤣