Rav Aviner was quoted recently (link) as saying that wishing “Happy New Year” on Jan 1 is prohibited because the Xstian new year is connected with idol worship and wishing happy new year would be a positive acknowledgment of an idolatrous celebration.
I e-mailed (though I’m not sure I had the right address) the ba’al hablog to see if it was possible to get some more information or clarification on this psak. I am curious as to why Rav Aviner defines the new year as a religious holiday and not a secular or civil holiday. The origin of celebrating Jan 1 as the start of a new year goes back to the Roman Empire, long before the rise of Xstianity. For centuries the Xstian world celebrated March 25 as its new year, not Jan 1. The establishment of Jan 1 as the new year on the Gregorian calendar may have more to do with this Roman precedent than religion. Jan 1 is celebrated as the start of a new year in countries like China, where it seems to be only a secular, civil holiday, as other dates are celebrated as the start of a new religious/traditional year (i.e. Chinese New Year). Interestingly, Wikipedia identifies Israel as the only country that does not celebrate Jan 1 as a new year.
Update -- I received the following reply from R' Friedfertig, who writes up the torah for the Rav Aviner blog, and am posting it with his permission: While it seems that the date was originally established for a "secular" purpose (although it is hard to know if it was not connected to idol worship in some way), in Western countries it is clearly part of the calendar which is related to Christianity. Rabbenu Ha-Rav Tzvi Yehudah was adamant that we not use the Christian date because of its association with idol worship and obviously saying "Happy New Year" would be included in that.