The answer can be simple and complicated at the same time. Ask your self this-was the event voluntary or mandatory? If it was mandatory, or there was a perception of being mandatory, you are covered. If it was purely voluntary, then you may not be covered.
If you have questions, it is best to contact an attorney with all the details. Workers' compensation cases are very fact specific.
All in all, have fun at the holiday party and stay safe! Perhaps lay off the egg nog.