In America, we live in a time when our stock as "Christians" is trading at an all-time low. We just don't have a generally positive image in the eyes of most non-believers. Gabe Lyons wrote an entire book about this. Here are some of the reasons I don't use the word "Christian."
1. It has a generally bad vibe. When I lived in the Middle East in the late 1980s, I learned very quickly that "Christian" did not communicate in a way that was likely to make people warm up to me very quickly. The word was weighted down with a lot of historic baggage. Now in America I find myself in a similar situation.
2. For many, it has come to represent a person who is against something rather than for something. While there are many things I am for and many things I'm against, I'm smart enough to know that I will never have a chance to be winsome if I am only known as the guy who is opposed to x, y or z.
3. As an adjective, it makes for funky theology. Many things have been marketed to the faith-based community by putting a stamp on it. The stamp is usually includes "Christian" or "Jesus." By simply attaching a label, does that make a video game Christian? Or a song? Or a film?
4. It is more productive to talk about the kingdom. Jesus spoke about it a lot. It is a big idea that invites people into our community so they can taste and see something good. When it comes to referring to my faith-perspective, I usually identify myself as a follower of Jesus (or something along those lines).
5. We should be thinking about the whole world and not just those who are already in the family. "Christian vs. non-Christian" tends to create an "us vs. them" mind-set. When we think in terms of the kingdom we can think in terms of how to connect in such a way that as many people as possible can experience the light and truth of Christ.