Last year when I flew with SQ ex SIN on Christmas Day in Y Class there was a special Christmas menu with turkey and Christmas pudding for dessert. The menu was also specially printed in Christmas colours.
The lounges had Turkey and Honey baked ham.
All SQ aircraft also have Christmas decorations on the aircraft for the month of December.
http://www.singaporeair.com/saa/en_U.../Christmas.pdf
Singapore Airlines -- News Releases
There is also a special Chinese New Year menu for flights departing during the week of CNY.
Regarding the rude cabin crew on the Christmas Day flight (I presume it was QF) I guess they also had a terrible time with the weather delaying the flights all week.