I was at the store the other day when someone did not get the greeting they felt they should have gotten. The clerk said to have a good Holiday but the customer was upset that she was not wished a Merry Christmas and said so.
To me that was rude and impolite. There is absolutely no reason to create conflict when none was intended. If someone says to have a good holiday, seasons greetings or one of the many other greetings you may hear this time of the year, consider the spirit it was given and respond with your own greetings, Merry Christmas. That is all that is necessary, that is all that needed to be said.