"Merry Christmas everyone, oops, I mean Happy Holidays". 

What BULLSHIT that some co-workers are now offended if you wish them a Merry Christmas.  Get real.  Christmas is not a swear word that I should be worried about being overheard.  If someone wishes me a Happy Hanukah or Happy Kwanzaa or even Seinfield's Happy Festivus, I don't go running into HR complaining about being insulted.  Lighten up people or Santa is bringing you nothing but coal.