You’ll find that most Argentine people tend to dress up a little more than what you might be used to back home. You will see young men wearing jeans and t-shirts or soccer jerseys, but you’ll also see a lot of people in nice pants and dressy shoes. Women tend to wear very feminine clothing, even if they’re wearing jeans, and they don’t tend to wear sneakers. Most people get very dressed up to go out at night, and you will probably want to, as well.
If you want to fit in a little better with your Argentine peers, don’t wear athletic-looking sweat suits or your pajamas. Nice, fitted clothing is what most people wear, and that is a sure way to blend in as best you can. Of course, as with everywhere in the world, you’ll find people who dress differently, maybe more “punk” or more sporty. The main thing that you might want to avoid is dressing like a “typical foreigner,” in baggy jeans and sneakers every day—at least until you get a better idea of how comfortable you are in your new environment and with your new friends.