1. A girl having very very small boobs. Her 'chest' would look just like that of a 'man'. So its called 'man-chester' OR
2. A girl having no boobs at all. Thus her breast are like that of a man's chest. Hence Manchester.
1. Yo gal! U so thin! U r just like a manchester!
2. Wear a padded bra gal. U ain't got no boobs. People myt call u a manchester!