When in company and I don't understand the topic I might initially ask the basics to a) get a quick leg up in life and understanding, b) let people know they shouldn't expect me to make any meaningful comments from this point forward and c) let them know it's ok to carry on.
When I'm out of my depth (happens more frequently than I'd care to mention) I have learned to shut the f**k up. A simple rule but much appreciated. I have been lucky enough to mix with some amazing, well known people in society. I try not to intrude on their mental space and tend to let them take the lead or set the tone. I probably would have made a good butler. In fact I'd have made a great butler - a very attentive sort.
On this board I'm aware my vocab and use of the English language is generally poor. I try, and at times I punch above my weight, but rarely. I bet if you looked back at all my posts you'd notice a unique style. A uniquely backward, repetitive style. But I'm better than I was five years ago and five years before that. It doesn't bother me in the slightest when I don't understand threads. Sometimes I use Americanisms to help the main readership across the pond understand more easily what I'm saying.
mmxiv