Ah I see. Yes that's a tough one. If I may offer some advice, try not to have an "argument", but rather a discussion. Arguments get nowhere, but discussions lead to more depth and meaning. Also avoid calling hypocrisy, as I mentioned before we are all hypocrites to some extent, so if name calling comes up just ignore it or request that the conversation remain respectful. If the discussion goes nowhere, that's ok and you have to be prepared to walk away without getting anywhere. As far as the truth goes, there is only one truth, but sometimes we all have different opinions of what it is. I personally believe that Jesus is the way, the TRUTH, and the life, and as such if He is portrayed in these discussions the way that He has commanded by spreading the good news, the truth will be made known naturally. However, keep in mind that God will only work the way that He wants to work, and if things work out differently than we hope during these discussions then just know that God is sovereign over all things and His will will be done regardless. It may also just take some time, as God does not work on our schedule. This is just my position as a believer, and others (like PMH and many others both on this site and elsewhere) are more than welcome to wholeheartedly disagree with me. But, I know for my own sake that I am saved and nothing can change that. All we are commanded to do is shine the light, it is up to each individual as to whether they follow or not.
All that make sense? Forgive me if this is too forward or not what you hoped for. I'll pray for your efforts :)