Three words: Document, Document, Document. Document dates/times and a short narrative for each incident with facts only. Don't insert your personal feelings, speculation or rumors. Then, my advice is to take the documentation to your direct supervisor first. If this RM is your direct supervisor, then HR is a good next step.
And please know that no one is a peon. Every person and position in a company adds value to the organization. If you or anyone else feels undervalued, then perhaps you aren't in the right organization.
Good Luck!