No one should have a "right to not be offended." Being offended is subjective. It has everything to do with you as an individual, or as part of a collective, or a group, or a society, or a community; it varies due to your moral conditioning, your religious beliefs, your upbringing, your education; what offends one person or group (collective, society, community) may not offend another; and in the final analysis, it requires one person to attempt to read the mind of other persons in order to anticipate whether a specific expression or perception will cause offense in the mind of another. And no, codifying an action in law is not in any way sufficient... it is well established that not even lawyers can know the law well enough to anticipate what is legal, and what is not. Sane law relies on the basic idea that we try not to risk or cause harm to the bodies, finances and reputations of others without them consenting and being aware of the risks. Law that bans something based upon the idea that some group simply finds expression objectionable is the very worst kind of law, utterly devoid of consideration or others, while absolutely permeated in self-indulgence. It is, in the end, something that encourages weak-mindedness.
Conversely, when people are truly harmed (not just offended) without their informed consent (and legitimate defense is not the cause), then the matter is one that should arguably be considered for law. Otherwise, no.
Your story depicts consequences of concerted psychological warfare upon an incompetent individual. Harm is possible. informed consent is not. Special care that does not apply in general society is called for. This is why your example completely fails to make your point. What applies to competent individuals is not particularly relevant to what applies to those not competent, whether that be because they are biologically deficient, or simply too immature to attain that level of sophistication.
What you want, in the end, is that no one can be offended by expression or perception within the context of normal society. If you allow society to pursue this course, you will end up being unable to express yourself, for I guarantee you that almost anything you can say or do will offend someone, and likely grievously so.
Either you take the attitude that others must deal with the ideas expressed to them or within their ken, or you begin to muzzle yourself -- and everyone else. Benefits would definitely accrue to those who wish to be coddled, but everyone else will suffer. Free expression is important. It is definitely more important than the possibility that someone, or many someones, might be offended. If that's not how you see it, then we have no common ground where a meeting of minds could take place on this issue.