It's the freshmen who are friends with people 3 weeks after they meet them.
Here's the deal: I move slowwwwwly when it comes to friendship. I may be in every class with you, eat lunch with you all the time, and study together, but I almost certainly won't consider you a friend until we've weathered at least a year together. (Frequently even longer - I only started saying I had friends here at HU recently, at the beginning of my third year here.) Nor does this have anything to do with how much I like you as a person. There are people I connect with and tend to like very quickly - that doesn't make them my friend. Even if they connect with and like me quickly as well. We're still just friendly acquaintances.
Part of the reason for this is that we don't really know each other yet. Unless this person has crazy mood swings or you've caught them in the middle of an especially up-and-down time of life, 3 weeks is not enough time to see the darker side of someone (or, for some people, the lighter side). There are people that I have liked instantly and then as I spent time with them more often in more situations, I realized I really didn't like them at all - they were cruelly judgmental, or they didn't like to listen to other people's points of view.
Just as I need to take that time to get to know them and all their ups and downs, I feel like that time's important for them to get to know me as well. I'm equally uncomfortable when someone considers me a friend in that short period of time. I had someone once inform me just a week after they met me that they thought I was one of the most awesome people they ever knew. Well, that's just silly. They'd only seen me in one light. They'd seen me when I was cheerful and chatty and entertaining. They hadn't seen me get whiny because I was scared, or say something really awkward and then obsess about it, or shut myself up in my room because I didn't want to talk to anyone (disclaimer: obviously I don't really consider that a bad thing, but whatever. It's perceived as such). If they don't know who I am to judge me in that period of time, how can I possibly know who they are and judge them? How can I consider myself friends with someone I don't really know?
Maybe some of these people are good judges of character and they sense better than I do what people are like... but I know for a fact that some of them don't, even when they think they do. (I had a weird experience where someone who called themselves my friend but didn't know me that well ended up with a very bizarre idea of who I was. Not bad things - just incorrect. When I told my group of close friends the ideas this person had about me, they all started cracking up and agreed it was entirely inaccurate.)
The fastest I ever made friends was when I worked with NLDC, where you were with some of these people every second of every day for 10 weeks (minus bathroom time and any days you wound up staying at a host home by yourself). Even then, my closest friends were almost all people I traveled with multiple times.
I guess I don't really begrudge people 3-week friendships... I just don't understand them. They make me nervous. I don't want to be in one.
Anyone reading this, I'd be interested in hearing your thoughts. Do you claim friends quickly? If so... why, or how, or what makes that decision for you? I'm sure some of this probably has to do with the extrovert/introvert breadth vs. depth distinction (explained here in a Google Books link to Adam S. McHugh's Introverts in the Church), which has always been harder for me to understand from the extrovert's POV.
I need a good ending for this post and I don't have one, so here's a Broadway finale for you.