Glitter,
Of course you can sing Happy Birthday! Think about it....what are you going to do? I suppose you could just stand there with a stupid fake smile on your face....or you could pretend to have to use the bathroom>very suspicious. Maybe you could get full of fear and put on an angry face>why go then?
Seriously, I had those initial jitters as well BUT there is absolutely NOTHING wrong with the words to Happy Birthday. Actually the silly lyrics are a bit on the drab side. You have nothing to worry about! Except of course the blowing out of candles and making a wish to some fairy. I have to admit, in my house we skip that part....the wish...(.not the candles).........we say a prayer instead, thanking God for the person to love.
It is just plain fun to show someone love. There is no LAW agaginst love......have fun.. dj