Known short for JMS, it is an affliction where generally young, Jewish women begin taking on many characteristics of a married, older Jewish mother.
Avi: I think my girlfriend has Jewish Mother Syndrome.
Chaim: What would make you say that?
Avi: Well when I don't eat her cooking she guilts me by asking if I think I'm too good for her.
Chaim: Bummer, man. Dump her for a shiksa.