Usually a business will fire an employee if they have either clearly broken a workplace policy, have committed a serious crime or have performance issues.
However, it is more likely a sacking will occur when a policy has been broken.
These can relate to occupational health and safety regulations, sexual harassment or even privacy. You are right to expect a reasonable level of behaviour in your workplace, and if this is not being met, following a number of warnings, you may be able to fire the employee.
Some of these grounds could include theft, fraud, violence or the threat of violence and breaching health and safety policies.
Also consider policies around information technology and what staff are, or aren’t, allowed to share over corporate networks and the internet. Breaches of policy could include sharing pornography over a network, or giving out other inappropriate material.
Monitor the use of social media. Following some recent legal cases there are now grounds to fire staff based on comments made on social media – especially if those comments are made during work.
Make sure these policies and procedures are clear, documented and are known to all employees. No staff member should have an excuse if a workplace policy is broken.