Is it permitted to attend the office ‘holiday’ party? Everyone knows what holiday this is for.
A Jew should not take part in such a party, because it is a party celebrating a holiday that to us is idolatry, (although if thier religion is actually idolitry like the Rambam or not, is not the issue) as it is not within our beliefs. Surely we may not actually partake in a party that is celebrating it.
Even if the person is not doing it to celebrate the gentile holiday, we are commanded not to go in the ways of the nations, which means not to do things that they are accustomed to doing for their religion.
By not attending and respectfully explaining that an x-mas party is not in line with your religious beliefs, it is very possible that you will be gaining the respect of the people in the office as a person that stand for his values, while having respect for others.
Tosfos Avoda Zara 12b “v’ey”, ibid 11a “v’ehi”, Bach Y:D 178, G”ra Y:D 178-7, Tractate Avoda Zara 6a,