Jewelchild, you offer a wonderful description. I wish that everyone that struggled with an "irrational" INFP would read your post, as you pretty much explain what goes inside our mind during such moments, and why we can freak out the way we do.
1) A letter is better than nothing. However, try to use it as a sort of training wheel to verbal confrontation.
2) Realize there are many ways to go about confrontation. A couple of quick ideas for you:
- Confront as soon as possible. As soon as you feel the 'tinge' of something amiss, say something. Just blurt it out. After two or three successes (and perhaps a failure), it'll get easier.
- Ask questions. This is a personal favorite. When someone starts upsetting me, my first reaction is to ask questions. Not only am I gathering more information to understand where the other person is coming from (and possibly realizing I just misunderstood), but I'm buying myself time to cool a bit before confronting them. Finally, I'm "hearing them out", which helps to disarm some people and make them willing to hear you out in turn.
- Don't take it personally. This is very, very difficult for an INFP. You won't be able to stop the initial blunt trauma, but with work you'll learn how to quickly get back up, separate your values, and go into 'ask question' mode. Let Te shield you.
- Reframe your views on argumentation. I know it's a long thread, but I think you could learn alot about how ENTPs view discussion. Notice how it's pretty much never personal for them at all.
http://www.typologycentral.com/forums/nt-rationale/16279-role-argumentation-entps.html
Soooo many good tips! Yes, a little hint along the way is much better than a blowup on paper later. And the other person will always have the letter as "evidence" and can nitpick it to death if he/she doesn't take it well.
Excellent advice from Udog.
I don't like confrontation either, but I've learned that it's necessary to take care of a small problem before it becomes a big problem.
In many cases, I would enjoy a letter over a verbal discussion. But, since there's already some type of disagreement or misunderstanding, a letter sometimes goes into too much depth about one person's perspective. This can be frustrating if the problem is misunderstanding in the first place. It just depends on the situation. Usually, an immediate discussion (but at an appropriate time and setting) is the best communication.
This is important to remember. And lots of times, a letter about a grievance can sound too much like, "This is how you are making me feel, and something must be done about it," which is much more self-centered than an actual conversation would be. Try not to focus too much on feeling language if you're talking to a T, as well.

Remember that sometimes you may be building up the importance of the issue in your head, assuming that the other person means you ill will, when they might not be aware they're doing anything wrong at all. It's possible that a very casual, lighthearted, comment in the spirit of, "Hey, knock it off, will you?" will do the trick.
I have a couple of friends with whom I "argue" best via text. It's casual, it's quick, and doesn't feel like an Important Argument Wherein One Sits Down and Evaluates One's Relationships, etc. I wouldn't have thought, "Hmm! I think I'll confront this person via text now!" I just needed to mention something to them, and it seemed less confrontational than calling them just to say something negative. This wouldn't work for everyone, but some relationships lend themselves to that medium. My roommate and I discuss important things much better in text than face-to-face, because we do care about each others' feelings, and we feel weird discussing things like that one-on-one. I don't know why. We're weird. It works.
JAVO said:
I think making "owning" statements of your thoughts and feelings is a good start in verbal discussion. Such as:
"I feel rejected when you don't talk to me in the morning."
"I think we might both be happier if we spent less time on the Internet. What do you think?"
Yes, but even better than that is to wait for an opportunity when the conversation is leading there anyway, and slip it in. Those "I feel" statements don't always hit me right when they're out of the blue--sometimes they just come off as needy. I'd be more receptive if I was talking about feeling like I don't have as much time in the day as I'd like, and THEN my friend could suggest that maybe spending less time on the internet might make me feel like I had more time. My mother makes statements like, "Why don't WE," when she means, "Why don't YOU," and it doesn't usually work on me.
Yes, I suppose a letter is better than nothing, but taking the time to put it in writing for someone tends to amplify the level of affront taken by the second party. It also doesn't allow for immediate feedback, nor are either party able to observe facial/body expressions as ques to the feelings behind the words. A simple example - Tell somebody they need a bath on paper, and it will always come off as condescending and rude. In person, and your vocal inflections/tones combined with your body language can make the same exact words come across a hundred different ways.
That said, if two people are in an irrational state of mind, they should stay as far away from each other as possible. Perhaps it depends on who your confronting?
Sooo true. If you've taken the time to write me a LETTER about something you don't like that I'm doing? It's going to make me think you've been sitting and stewing on this for ages. It's much better (for my personality, anyway) if you try to make it a more casual suggestion. Or jokingly let me know that it bugs you when I do x.
Writing letters is MUCH MUCH MUCH better than doing nothing and letting anger fester until you explode.
Remember that most people are not nearly as good at emotion-reading as you are.
That said, direct conversation is preferable, but if you really can't manage that then I'd say the letters are okay. The best you can do is explain to your family/friends that you're not good at putting your complaints into verbal words and that letters are the only way you can organize your thoughts.
This may be difficult for them to accept at first, but it's definitely far preferable to just never saying anything. Many an INFP has randomly exploded on someone for things s/he didn't even have any idea were a mounting problem.
Yeah, I would definitely preface it with the reason why you're writing instead of talking. And writing is definitely better than exploding out of nowhere. BUUUUUUUT. I wouldn't want to get a letter every single time my INFP friend had a problem with me. Use it sparingly, if you do.
One more thought: If you are in a situation where you have to let someone go at work or you're breaking up with someone, you owe it to that person to say it to them face to face, or at least over the phone. Writing a letter/email would definitely be the cowardly way out in those scenarios, IMO.