Assalamualaikum.I give you two ideas.1. Give that 100 bucks to poor people through your office with intention as sadaqah, not as a part of Christmas celebration. 2. Try to find a reason not to give money before or during Christmas celebration, and then you give this sadaqah after the Christmas celebration has over.But remember, these ideas are not fatawa because I am not competent to issue a fatwa. You should ask your local Imam, which idea you can implement. Or if your local Imam has the third idea, you can follow his idea.Muslim are allowed to give sadaqah to non-Muslims, and even Muslims who able to give sadaqah are obligated to give sadaqah to poor people around them, Muslims and non-Muslims(*). So, whatever alternative you take, you still have to give money to poor people around you. Not with intention to avoid you from anti-social mark because if you give sadaqah with 'not-sincere' intention like this, your sadaqah would not be 'accepted'. (*) there are some fatawa that forbade Muslims give sadaqah to non-Muslims who fight Muslims/Islam. But I believe, poor non-Muslims people around you are non-Muslims who do not fight Muslims/Islam.