Hey, not_stupid,
Unlike the Prude and a few others around here, I'm going to cut straight to the chase of your letter:
I've maintained a standard of excellence in my academics and extracurricular activities, but try to let my personality speak more loudly than my résumé. How can I let my friends know that their comments are hurtful? Should I be worried about my reputation? If so, how can I repair it without coming off as a braggart or a bore?
I am going to assume that the first part of this is true. That's not totally taken on faith because your letter and the comments you have made here show you seem to be a bit more together than the average freshman I have dealt with over the past 30 years of working on a college campus. (If that statement is NOT true, if you have not maintained high standards both in and out of the classroom, then I'd do some serious reevaluating if I were you).
First the friends: Are you SURE they really are friends? If they can't accept you as you are, then maybe it's time for some new ones who can. While developing friendships in college is important, it is far from the most important thing. Even though it was eons ago, I still remember that "freshman corridor". Dorms were still single-gender back then. Most of the girls on my floor were catty and way too willing to peck at those they felt didn't measure up to THEIR standards. Not too many of them made it through college (and, yes, while the place wasn't an MIT, it had more than it's share of brainiacks with 1 in 4 women being valedictorians of their high school class - guys weren't quite so "smart"). So, evaluate them individually as "friends". Figure out which are truly of value, then talk to them about how their behavior (often this kind of thing is a "pack" behavior. The ring leader does it, then the rest follow along so as not to be left out) bothers you and ask them to stop. The true friends will. The rest aren't worth devaluing the term "friend" on.
Second, the reputation: Are you looking at short-term reputation or long-term? The long-term one IS going to hinge on that resume and your transcripts, NOT what your "friends" say about you. So, keep up the grades, assume leadership roles in the clubs/organizations you are involved with, get in some community service, and keep track of it all so that when that long-term reputation IS the key one, you don't forget about things like that weekend you spent cleaning up a neighborhood park the beginning of your sophomore year.
The short-term reputation goes back to picking the right friends now. Get rid of the fluff. Develop the good ones even more. Get out and meet new people through those extracurricular activities, ones that you will have more of a connection with than just living on the same floor or eating in the same dining hall.
As to the drinking, you do it to have fun, right? Well, if you truly are having fun while you are drinking, you'll want to remember that fun down the road. As long as you are drinking only to the point that you can remember the fun you had, and can laugh about it the next day or a few weeks later, you're probably not drinking too much. I always feel sorry for my students who come in on Monday bragging about the great weekend they had but can't remember a thing because they got so drunk. When the same student tells me that more than a few times, they get the "maybe you shouldn't be drinking so much" lecture. If you can't remember what you did, find somebody on your campus willing to give you that lecture when you need it.