Only at Christmastime can you sing and dance along to the radio, loudly, in Tesco car park with your sister - and be clapped
Only at Christmastime will a card come in the post from someone you haven't seen nor spoken to in nine years, without a return address
Only at Christmastime does generousity get the better of you (and your bank account). groan.
Only at Christmastime is it ok to laugh at your music teacher in church, as he uses his grade 5 piano skillz (and forgets to play the last verse of Hark the Herald...)