Lyric discussion by eldantastico 

In the course of a man's life, especially nowadays, we go through a lot of different relationships. When I look back at the girls I've dated now, I realize that some girls mean more to me than other girls do- 'Some girls are bigger than others'. And this one girl especially it seems will always be bigger than the others. :( So to me this song isn't about the physical size of a woman but rather the size of the feelings and emotions that you have for them. And that is the genius of Morrissey..

This is one of the best interpretations I've read. I have nothing to add except that if someone felt that way, they should act on it before it's too late):

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