I can relate, a lot. Even speaking up doesn't usually help. especially if you get "shh... just a minute. " or "quiet, the grownups are talking" (that 2nd one is paraphrasing, that is not *literally* what they say. But it is what they mean.)
I recommend something I'm trying to do myself right now. Have a list of things to repeat out loud every morning.
First, attitudes you need to remember and practice.
like:
* Never give away Too much information
* Never apologize for asking a question
* Don't get caught up in Stockholm syndrome / Don't fraternize with the enemy
or whatever attitudes you know you need to remember / practice
Second, lists of phrases you can have at the ready. Things you never generally say, but then later you wish you had
like:
"Do you really think you are the only one trying to get through the hallway"
"You have completely misunderstood my point"
One useful one for me has been:
"OK, you try that and let me know how it works out for you."
Like when people give you crap like "that is why you should always do such and such... " (and it is stuff that was too obvious, they missed the point, completely, or you have already tried what they were suggesting.)
The important thing is, find out what items work for you, repeat them out loud every day, and you will have an arsenal at your ready, so that you will be more likely to say what you should have said, at the right time.