We took a personality class in my psychology tests and were talking about introverts and extraverts.
I've always seen myself as the former. I tend to keep to myself, not be very social. Sometimes it's because I'm shy. A lot of times it's because the people involved in whatever are simply not interesting to me. I also don't like large crowds, for various reasons.
The interesting thing is that when I mentioned this in class, most of the people in it were surprised and said that they saw me as very much of an extravert.
They didn't back it up with anything, but I think I can see where they were coming from. I'm very active in the class - one of the the 4 people in it who always have something to say about whatever subject we're talking about, often joking, etc.
But I only get this way under certain conditions. Firstly, I need to have known the people I'm around for some time; and secondly, there need to be people in this group whom I actually like/admire, otherwise I see it as being pointless to 'come out of the shell'. And of course, booze works as a great substitute for the two =D.
On an even weirder note: I got a 10 out of 10 on the psychology paper I wrote for the class a few weeks ago. And all the while I thought it was a horrid paper not worth much of anything.
Moral of the story: Make people believe that you're an extravert, and you'll get good grades for all your shitty papers! ;)