'Amhran na bhFiann' isn't sang by most people at Ireland games because most people don't know the words. Plain and simple.
Getting funny looks if you do sing it is just other people's way of getting round the undoubted discomfort they feel at not being able to sing along themselves. And believe me, they feel that discomfort. There's a lot of bowed heads and shuffled feet that goes on during the anthem, particularly for that reason...
It's nothing short of an embarassment that the majority of Irish people do not know their own national anthem. I can't think of any other country in the world where such a situation COULD possibly arise, let alone does arise.
The same with the flag - feckers will argue with you 'til their blue in the face that it's supposed to be green, white and gold.
I do believe that both the anthem and the flag may well change in the future as part of the solution to the Northern situation. Would be sad to see 'Amhran' go, but it's a small price for sorting the country out.
Just as long as we don't replace it with that Eurovision elevator music 'Ireland's call. Yeuch....
P.S. Noticed at the Scotland rugby game on Saturday that they flew the 4 provinces flag and cross of St Patrick above the stadium, but not the tricolour. The overwhelming majority of flags inside where the national one though.