I'm the sort of person who has trouble not saying what they think. It just rolls right off my tongue. That's not always a good thing. Learning to nod and grin would often be in my benefit, but I find it difficult to do.
How about you?
A bit. I'm naturally very polite and deferential to begin with, so it's not difficult or unusual for me to think about what I say before I say it. I think my self-censorship is pretty well built-in. Sometimes I reword or omit something. Occasionally I think twice and decide not to speak at all. I'm cool with it. Nobody cares what I have to say anyway, so it doesn't matter.
Where I get into trouble is those areas in which, due to my strangely poor socialization in early life, I disagree with the herd about what constitutes a socially-acceptible thing to say. Like, I don't see anything wrong with telling someone, point blank, that I disagree with them--no matter who they are. Some folks think that's rude. Or being honest about your strengths. Many folks will consider that boasting. I make trouble for myself when I breach these idiotic imaginary lines that others abide by and refuse to feel abashed when they try to call me out on it. Uh, no--im not playing your dumb game that sucks. And I'm not going to feel bad about it, either.
Most of the time say what is on my mind, yet also I am careful and seek to do this in a way that is not offensive, not only for the sake of politeness, but also because the other side is much less likely to act in the direction I want if I manage to offend him/her.