Ok, it wasn't exactly that, but it was the gist of the question.
I have to say, the question took me by surprise. At first I thought, well, Christianity is the religion that is specified by people who follow Christ. After considering that, I realized how vague and inadequate/unnecessary it was. I then thought, perhaps, as many contemporaries seem to put it, Christianity is a relationship. A relationship with a God who is invisible and infinite, by His incarnation as a human on this earth around 2000 years ago. My first reaction to that is, well, you are crazy. To think that God would become incarnate, would be restricted by flesh, by a stomach, liver, kidneys, and matter...well that is incomprehensible in my opinion.
Next, I considered that perhaps Christianity is a lifestyle. It is living by putting God first, and those around you second (on your list of priorities in life). But that is still so vague!
Of course, this all happened over the course of 5 or 10 minutes, and I ended up saying nothing in particular in response to his question. But I appreciated it. He challenged me.
Is Christianity a religion, relationship, lifestyle, or something else entirely? Let me know what you think, and mayhaps we will have a discussion going on. I would like to hear your thoughts on this, that is why I am asking ;)