Arguing and refuting rarely convince anyone to change sides. I've learned to make suggestions or mention pro-freedom ideas if the chances arise without saying "libertarian."
Winner. I just make libertarian-leaning comments on things that are right in front of us and relevant. For example, my boss is a pretty damn hard-line conservative, listens to Rush, etc. We were in Louisiana on Monday visiting a few fields (of the oil variety) and at one point we were crossing a very long bridge over miles of swamp with .1 mile markers. I made the comment "I wonder who got the contract to put in those tenth mile markers". I didn't mention it again, but he mentioned it to five other people that afternoon.
EDIT: Oh, and welcome to the FTLBBS.