That means Extrovert meets Extrovert, Extrovert meets Introvert, and Introvert meets Introvert. I wrote this as a blog, but I guess I could post it here for discussion an relevant stories.
This is based on speculation and experience, but this is what I would say generally happens when E's or I's are with their own kind, or when they meet each other. Most people are going to be ambiverts (in the middle of E and I);however, I'm considering people who are blatant E's or I's here.
E meets E
Assuming they're friends E's generally have a lot of fun together and will generally like a lot of the same activities for the same reasons. They will also be glad to use each other's social networks to expand their own social networks. "Hey, I'd like you to meet my friend _____." If the person isn't repulsive to them, then they are happy to meet someone new.
Sometimes two E's will be insignificant friends with each other, and they're perfectly okay with that. Often times these insignificant connections are based around an activity like, "He's the guy I go surfing with." Sometimes they won't even trust each other, but that doesn't matter since the connection is all centered around an activity. Don't get personal. Don't make yourself vulnerable, and just stick to the activity, talk about the activity, and exchange small talk. E's are often okay with having some relationships like that if they also have some good ones too.
Sometimes it seems like E's are in a talking competition. They both have so much to say they could pretty talk on top of each other without stopping, but it would be incomprehensible if they didn't stop to listen to each other. Sometimes two E's can overlook necessities and responsibilities cause they're too busy having fun (EP types). If the E's have differences in personality or opinions, all hell can break loose cause the assertive E's are not at all unwilling to go at it with each other.
E meets I
This is usually a connection established by the E and can result in people being compliments to each other if other things are similar. One thing that is important to these types of connections is that the E understand how the I is different and respect that the I is different. It can help for them to make up in their minds that they're going to fill in where the I is weak and appreciate where the I is strong. E's will find I's aren't interested in as many people, and that they really value one-on-one time instead of time spent in groups. E's must respect the I's need to be alone, and I's must respect the E's need to be around people and to have fun.
E's will find that I's are less driven to pursue things, especially the fun things that E's really like to do. The I may like surfing, skiing, or whatever, but they're less willing to exert effort to make the surfing or skiing trip happen. As an E you may find you're naturally the driving force that makes such things happen where as the I will appreciate you for making it happen because he knows he wouldn't do it himself. The I may enjoy some excitement, but he does not have a need for it like the E does.
As an E imagine you're going through life as an impatient driver who's in a hurry and going well above the speed limit hoping he's not gonna get a ticket while the I is more like an old lady who's taking her time, driving under the speed limit, and trying not to get killed (not saying E's and I's actually drive like this cause I don't drive slow). The E and I connection can serve as one where the E causes the I to speed up a little and the I causes the E to slow down bringing them both to the proper speed limit. E's are generally enterprising in some way, whether it be business or socially where as I's sort of just float through life and take or deal with whatever happens to come their way.
The E and I connection can be good because the E likes to talk, and the I, being less inclined to talk, ends up taking on the listener role as opposed to the E's talking on top of each other situation. The E can contribute many things to the I such as other people met through the E and activities the I wouldn't have gotten involved with otherwise. The I can contribute loyalty and stability to an E who's got many disposable and replaceable people in his life.
Problems occur between E's and I's when they don't respect each others differences, but even if they do, sometimes things just naturally get out of order. E's can talk too much and do too much, and the I will be overwhelmed as a result. I's can fail to carry their weight in conversations and be too boring for the E's. There can be a lot of differences in interest from being willing to go to parties to even types of music. Generally, E's and I's need other personality traits to be similar or some clear areas of agreement or things will not work too well.
I meets I
This, unfortunately, is the most rare occurrence possible. It can be hard for I's to befriend other I's, and generally, there needs to be an obvious point of interest or practical purpose. When two I's become friends it can work great, though. I guess you could say they see I to I. I actually have lots of experience with this having an I-T- brother.
I remember how we were in a band, and we had to drive to New Orleans to practice or play music. On those drives of over an hour, we'd go in and out of talking and were perfectly comfortable with it. When we noticed the conversing stopped, we'd turn up the music. When we had something to talk about, we'd turn it back down. There was never any threat of either one of us being overwhelmed by too much stimulation, and we both just existed as introverts as comfortable as could be..The tricky thing is trying to get a relationship like this established if you're dealing with two unrelated people. It takes time to get comfortable with someone, and generally, communicating is a necessity. Sometimes I's are in a perfect situation where they could be friends, but both of them fail to stir up enough conversation to make it happen. If a friendship is established, things can end up getting too predictable, repetitive, and boring for some of them (although, some of them would be okay with that). It's possible that two I's could have some significant things in common, but they never find out because neither one does enough digging to get it out of the other.
An area of similar interest can really help an I relationship form and last cause the activity can fill in all the silent time. If they're low in openness, perhaps they could repeat the same activity every time such as ping pong, and if they're high in it, they would need an activity that's got potential for new developments and changes such as playing music or playing video games. They could also try to find new activities they both like.