You are right, no cuss word changes that.

But, what that boy did could show you something, I think atleast. It is all about being Christ-like. Where I live, cussing is not a very christian-like things to do (lol, neither is liking boys). The truth is, if I was to meet you and I knew nothing about you whatsoever and a cuss word was one of the first things I hear from you mouth, I would assume you were not a Christian (and i know I should't assume, it is human nature), although you still could be. It is like school. If you are walking down the hallway and a guy with black hair, black clothes, etc. walks by, would you not assume he was a 'gothic'? If another guy walks by and he is wearing an abercrombie polo shirt, blue jeans/khakis, etc., would you not assume he was 'preppy'? Whether or not the guys actually are what people assume, they are thrown into that group because of their external appearance. And then, if a group of guys walks by and you hear their conversation and within it you hear cussing, what do you assume? It is all about association, and sort of stereotypism whether it is right or wrong. Even if you don't assume those things, other people do, so you have to think about what people see and hear you do, and what they will think about you from what they see and hear.

And even if none of that applies to you, do you think Jesus would have cussed? As a christian we are supposed to be different from this world, we shouldn't want to be like this world, for it is not our home. And if cussing is something the world accepts, and it is accepted, just watch TV, then should you accept it?

Also, instead of getting mad at him, why don't you explain to him that cussing will not make you loose your salvation. Obviously he has been taught that cussing is a bad thing.