Social settings: I hang around a lot of INTJs - I studied engineering in college and I work for a R&D technology company now.
It's good to be among 'my people'.. . lol
On my free/private time, I don't really socialize a whole lot nowadays, but I used to be very social with a tight-knot group back in the days - we met pretty much daily for coffee and discussions. I have a 'lunch crew' here at work. We meet pretty much solely at work, but we have grown very close to each other.
On the rare occasion I do socialize after work, it's with people I already know pretty well and me being there is almost always based on 'social loyalty' - like a friend has a birthday party and I feel I ought to go. I have learned that I really dislike getting to the social event, but when I am finally there I enjoy myself a lot and think to myself "Why don't I do this more often?"
I like book-stores, cafes, restaurants, nature, parks, museums, the internet - places where I don't have to interact too much with strangers, if I choose not to.
Discussion subjects: I am very adaptable, so I can talk about pretty much anything, I enjoy bouncing around ideas and thoughts with people who see things from a different perspective than I do. I like deeper analysis of things, especially people.
I am fine with just hanging out in silence too.
And I actually do like to joke around quite a lot - laughing is great and a good way to bond in an nonthreatening manner. You can learn a lot about people based on their humor.
Subjects to avoid: Areas that can be too personal. I am fine with my friends volunteering information, but I would never pry - you want to share, I'm thrilled. If not, you have your reasons. I am painfully honest and open myself. lol
I'm not big on politics or religion discussions irl here in the US, since it always seems to lead to conflict/judgement. Interesting subjects, but I'm not into drama, so I'd rather not go there.
Quietness: I can be very talkative depending who I am with and depending on my mood. If I am around strangers, I can chit-chat for a little while, but it exhausts me fairly soon. I deliberately shut down completely around people I dislike. Quiet doesn't bother me.

As a matter of fact, quiet can be a great way to piss off people I don't like... ;-)