An objective investigation of the facts may find that company policy was violated and that the accused needs to be disciplined, up to termination if warranted. Similarly, an objective investigation may conclude that company policy was not violated, or that there’s not enough evidence to say for certain.
Legal standards measure against what a “reasonable person” would find offensive. But there’s no one “reasonable person” who can objectively tell us what is or is not offensive behavior. Some people can be touchy and over-sensitive; some people can be truly, honestly in the dark that their comments or actions are offensive. That’s why it’s so important to follow your company's written policies – they are a standard, applicable to all employees.
It is possible that the person reporting the complaint is being untruthful, retaliating against his boss or hoping to win a lawsuit. Your company’s investigation may find that the complaint is not only false, but also deliberately vindictive or malicious. In these cases, your supervisor can take disciplinary action against the complainant. Again, clear written policies will help protect those involved as well as the company, should this situation arise.