How are you being accused? Does the bartender call the police? If so, there is not much you can do to stop him. Does the bartender make statements to other people? If so, you can sue the bartender, and perhaps the bar, for defemation per se. Two issues are whether there are large enough damages (or any real damages) making it worth while to sue and whether there are assets to collect from.
I am a former federal and State prosecutor and now handle criminal defense and personal injury/civil rights cases. Feel free to check out my web site and contact me at (212) 577-9797 or via email at Eric@RothsteinLawNY.com. I was named to the Super Lawyers list as one of the top attorneys in New York for 2012. No more than 5 percent of the lawyers in the state are selected by Super Lawyers. The above answer is for informational purposes only and not meant as legal advice.
Is the bartender the owner? If not then try talking to the owner and tell them what is going on and state that you can just start going somewhere else if it does not stop. Stress how long you have been a regular customer.
DISCLAIMER: David J. McCormick is licensed to practice law in the State of Wisconsin and this answer is being provided for informational purposes only because the laws of your jurisdiction may differ. This answer based on general legal principles and is not intended for the purpose of providing specific legal advice or opinions. Under no circumstances does this answer constitute the establishment of an attorney-client relationship.
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