I do this all the time. Some times I will only have the conversion in my head and never bother to have it with the person in question because I feel that I have already covered the ground and I know how they will respond.
All the time. I also end up pacing around the room at the same time, which is apparently amusing for anyone who walks in on me. If I'm doing it with someone I know well and I'm comfortable with whatever topic it happens to be, I'll occasionally bring it up to see if I guessed their end correctly, though I mostly don't mention it.
I can't say that I have full conversations, but I do try to predict peoples reactions to things that I could say to them. It's kind of like one of those logic puzzles that involve a lying doorman and a truth telling doorman, and you have to ask them questions for whatever reason.
"If I say A to person B they will respond by saying C.." and so on.
I DO THIS ALL THE TIME. Especially if I have to reply to emails or stuff, I compose a really long email in my head, and when I actually sit down to write it, it feels like I've already said everything I wanted to say, but I haven't said a word, so it feels repetitive, and then I go procrastinate and do something else... and... um, I believe I've answered the question.
For the longest time I found that I was essentially 'having conversations' with people that I knew, trying to figure out what their response would be to something I asked them... all in my head.
I would run through all of the different possible reactions, (sometimes getting myself so worked up by their responses that I would literally feel sad, angry, etc) and then decide which one they were most likely to give me... AND THEN NEVER ASK THEM THE QUESTION! I would move forward as if we had the conversation
Crazy-Delusional, or INTJ-ish?
I have done that and I'm totally NF...and E. Perhaps the difference is eventually I will have the conversation I need to have because it's not fair to the other person..even if I'm almost competely sure the convo will turn out as I thought. I have to take a step away and watch myself during the actual convo because I don't want to manipulate it to go the way I imagined...
for my life is slowed up by thought and the need to understand what I am living.