If the gym coach hurts people with nails, it is unacceptable behavior, and appropriate measures need to be taken to protect the safety of themselves and others. First, leave the scene immediately to ensure your own safety. Call the police to the relevant departments, report the incident to the police, and let them intervene in the investigation and take necessary legal actions. It is recommended to collect any possible evidence, such as wound photos and witnesses, to support your report. You can also complain to the gym management or related institutions about the coach's behavior and let them take corresponding disciplinary measures. Protecting the safety of yourself and others is the first priority. By calling the police and complaining, relevant institutions can be prompted to take action to ensure that similar incidents will not happen again.