If this happened I would ask why this person was offended by Christianity, and for the record aken, I think that a lot of criticism towards christians are fair game b/c the christians themselves haven't been perfect by any means.
I'm not sure who "this person" is in the context of your statement, I think you mean the offended party. But what i have to say is maybe you wouldn't be offended (though it's highly possible thats just what you say in context and in the actual situation your reaction would be different than it is here). But if your trying to say what I am saying isn't true I would ask if you remember the painting of Jesus made out of feces I believe it was for view at the MET in New York that had to be removed because of protests. Basically what I am saying is it's easy to talk bad about what others (who are different) do with out realizing that ones own reactions would be much more similar than one may be willing to admit.