Irecently discovered, over at uCatholic.com, a series of videos by Catholic apologist John Martignoni. These are great, quick defenses of Catholic teaching. If you're in an elevator with someone, or a news reporter confronts you as you are walking out of church, or you find yourself in some other scenario in which you have just two minutes to make your case, this is what you would say.
Here are his videos on Church authority:
For more by John Martignoni, see his Bible Christian Society website, which has a wealth of Catholic apologetics information.