I often found this happening to me during meetings. I just couldn't track verbally after about 10 minutes. In those cases, I just did the best I could, and often ended up overstimulated.

But I have asked people to stop talking, as I was having a hard time with sound. No matter how gently (or not) you say it, it doesn't seem to be well received. I think the easiest way is to always be prepared for an escape plan, hope you don't have to use it, and keep trying no matter how long it takes. It took me over two years of practice before I could usually eat lunch in a restaurant without too much trouble, and it's still not a guarantee on a bad day. But I can do it now.

Things like taking breaks from the conversation, earplugs, regular exposure, and sometimes just going home helped me until my brain could handle just a little bit more. Once I gave myself permission to not be locked in, it was much easier to deal with things without as much frustration.