Inappropriate Communication/unsupported claims

I work for a small city and my boss has told me more than once, that another department head complains about me during their department head meetings. These are complaints that are trivial that go from "she doesn't smile enough" to accusations of rudeness to others. Keep in mind that there are about 15 people in these meetings that are in charge of the various city departments. The City Manager does nothing to redirect the conversation. I don't feel that this person has a right to discuss anything about me in a department head meeting. If she has issues about me then she should go straight to my supervisor.

I've had enough and I'm going to file a complaint with HR to stop this innapropriate conversation. There have never been any complaints filed against me for being rude to a customer/citizen. The fact that I don't smile enough has nothing to do with my job performance,etc..I'm an accountant and tend to be serious in my work environment.

What legal complaint do I have regarding this issue? I feel she is being slanderous by the rudeness complaint and the smiling issue is being ridiculous. I just believe that discussing another employee in that type of meeting environment is just plain wrong. I can't prove harm for defamation purposes but I think there must be something to stop these types of conversations in department head meetings.

Any comments on this issue would be greatly appreciated.