If you ask me, there should be some regulation barring employers from forcing their employees from attending office parties after hours. I can still understand if it were some seminar or training sessions related to improving your work-related skills but when it comes to parties that doesn't contribute anything useful such as twerk dancing or heavy drinking, then it must remain entirely optional. Besides, many of your employees have actual lives outside of work, busy taking care of themselves or their families, if not having to pay the bills or rent so they can live for another day.