What does it mean to be in offended? If you look the word up in Webster, it means to transgress the moral or divine law. But that is not quite the definition we are getting at here. If you look at the etymology of the word, you discover it is Middle English > Middle French offendre > Middle Latin offendere to strike against, offend. It means to violate or transgress, to cause pain or hurt, to cause vexation usually by violation of what is proper. The word has a sense of personal affront, to hurt literally or figuratively. The concept of offense is located in the idea of violating a moral standard. In modern vernacular, it carries the connotation that one has violated accepted norms of behavior and thereby has offended the senses of others.
In order to understand what should and should not offend us then, we have to identify the normative standard by which we all should behave. However, in our culture, we find such absolute norms repugnant. This is because we are a non-thinking culture that wouldn't recognize an irrational argument if we paid $20 dollars for a ticket to watch one at the local iMax theatre. Yet, without normative standards for human behavior, offense is not a rational possibility. So what is a society to do? We invent our own! And they are different for each person!
And there you have it. Cultural relativism lends itself to the idea that no human behavior is safe from offending someone, somewhere. But isn't there some behavior that even a pluralistic and relativistic culure like our own can agree should not offend anyone? I think so. What about saving a human life? Do we think that would or should offend anyone? I think it is safe to say that acts of genuine nobility should not offend anyone. What about loyalty to one's friends and spouse? Should that offend anyone? Probably not! What about talking about one's belief in God? Does it offend anyone? Yes! What normative standard does it violate? The one that says you should never talk about religion publicly. And who created that standard? It certainly was not a religious person. You get the point.