Often an girl who suffers from Ugly Girl Syndrome is socially retarded. Using tactics such as being a slut she is able to attract a partner. Often she will lie and present herself in a grandiose manner in an attempt to distract a potential mate from her self perceived ugliness. Once mate has "fallin for" said UGS sufferer she will then self sabotage the relationship thus making her the perfect candidate for people not wanting a long term relationship.
John dates girls suffering from Ugly Girl Syndrome because he is not yet ready for a serious commitment.