An important part (but not all) of offensiveness is in the eye of the beholder. So the fact that you can't see how something is offensive should be good reason for you to be even more aware of the fact that others are offended by it.
Let me explain it linguistically, because you went there. Good and excellent are both terms of approval, but one is stronger than the other. There are times it would be appropriate to say that something was good but not excellent. It would be inappropriate because one of the terms carries a stronger denotation than the other.
Prostitute and a four letter word starting with an S are synonyms in terms of denotation, but clearly one has a very different connotation than the other. If you can't see how saying one of those terms around little children could be problematic, then simply heed these two pieces of advice.
First, for the sake of CL, those are the rules. If you break them, you'll be punished.
Second, for the sake of living your life, know that you'll offend people and people will dislike you as a result.