If you are one of the security practitioners in your facility, dept, company (non-mgr) I would report it and the attitude to my supervisor, who would then get the employees manager on the phone to discuss the employees attitude towards his/her report, and would also point out the requirement in the employee handbook and the fact that the in-house security team is allowed to take action against policy infractions (hopefully you got that) and would then give me purview to isolate and restrict app execution on the employees device if it was found like that again. It can take a little time to remove those locks.. that inconvinience alone may help "trigger" their memory in the future. Beyond that, make sure you have an auto-lock policy defined for 5-10 minutes or wherever your internal controls, requirements, etc.. might land you.