The one on December 26th? Not many of us here are from Sri Lanka, hence why we wouldn't know offhand (I have my reasons though ), much like how 9/11 is completely different for the Americans here than the Europeans.
True, but the act of 'commemorating' it consistently for 9 years sounds much more like a dangerous and violent grudge than simply sorrow for those who are lost, when you consider the numbers of lives lost in natural disasters, poverty, or vehicle accidents each year. We seem to be dealing with something far more sinister than mourning. After all, who remembers the date when Sri Lanka was hit by a tsunami?
There's a difference with those though. Natural disasters are beyond our control, while deaths as a result of poverty and vehicle accidents are and have been a constant throughout society over the centuries. 9/11 on the other hand, was a terrorist attack on a single day. It happened within the lifetimes of everyone on this board, and many of us remember it.
It really isn't a grudge either. Most of us aren't using this as an excuse to condemn everything that has to do with Islam. It's a day to honor those that died. If Wikipedia is to be believed it's actually less a grudge than the UK's Guy Fawkes Night historically was.