The 'X' in Xmas is taken from the Greek word for Christ. It is not blasphemous in the slightest. In fact, using the words Merry or Happy is seen as blasphemous. Christmas means 'the death/sacrifice of Christ' and saying Merry/Happy before Christmas is seen as very poor taste!
Christmas does not mean 'Christ's birth' as many people believe. Jesus was not born in December at all, he was born in September.
Happy birthday 
