It was hard to believe that a lot of my classmates in school were so close-minded. Many of them did not know that there were other religions out there besides Catholicism. I believe the most important thing about going off into public education for college is to be open-minded.
Part of my requirements for my graduate program was that I had to take an ethics class. Culture. Shock. While I was still in a rather conservative part of the state, there were always those rebels who hated their upbringing and wanted complete thoughts different from their parents. Political views often alternate generations; children always want to differ from their parents.
The only advice I can offer is to be open-minded when someone else's opinion differs from yours. Listen to their opinion; give yours. There is no reason, EVER, to tell someone their opinion is wrong. Opinions are opinions. Given the opportunity to defend your faith, do so justfully. Remind them that you were raised Catholic, so you probably have a better understanding of what the Church teaches.
Many of you may have seen the #SomethingIGetAlot tweets about stupid questions we get from non-Catholics. BE PREPARED for them. Not everyone understands Catholicism, be prepared to inform, not preach.
The best way to sum it up is that you are entitled to your opinion, and they are entitled to theirs. If you thing it is wrong for them to attack your beliefs, then it is probably wrong for you to attack theirs. That only adds fuel to their fires, allowing them to think that Catholics are close-minded and backwards.