I see myself as guarded, but not "too" guarded. I don't think being guarded is a bad thing--better safe than sorry. I'd rather not take a risk and play it safe than risk it all and lose it all. And I am comfortable with that arrangement.
I am very isolated when it comes to the social atmosphere of a place. There are days when I wake up, drive to school, attend classes, and drive home without saying a single word to anyone. I feel very disconnected from other people and don't like it when random people come up to me and start asking about me, and I find sudden questions about myself from some random person I don't even want to talk to while I'm trying to get to class or get home to be rather invasive. I'm very private outside of the forum setting.
It takes me a very long time to warm up to people. But once I've warmed up to them, they can't get rid of me lol. I've described myself much more than once as "easy to get along with, but difficult to get to know." I'll be pleasant (although secretly irritated) if you try to start small talk with me, but it'll all be pretty shallow conversation and you won't really learn anything new about me and I most likely won't be being completely honest (such as saying I like a TV show when I really don't in order to avoid dealing with backlash). The reason I had a reputation as an MMO heartbreaker was because I didn't really "know" any of those people who were telling me that they liked me, so I rejected them.
Honestly I do not know how I have the friends I have now. I will admit that I haven't made any new irl friends in almost 5 years now. I am the worst at meeting new people (and completely unwilling to try), and the absolute worst at staying in touch. Once someone has finally broken down my wall and befriended me, I'm not guarded with them at all. I overshare with them. In fact it's become such a habit that I overshare with my ISTJ that he gets kind of offended if I haven't overshared with him in a while, even though I always feel like venting to him bothers him, because he knows that all that chatter and nonstop "thinking out loud" type conversation (often times one-sided over IM) is just how I express my closeness to people.
tl;dr I'm super duper guarded and have lots of thick walls but have fun trying to get me to stfu if you somehow manage to break them down