Ahmad's explanation of 'goosht koobide' is good and complete but if someone impolitely calls someone else 'goosht koobide' he/she analogizes his/her face with 'goosht koobide' and mocks him/her

as you might know "ABGUSHT" is a traditional persian food too.it is basically made with meat ,beans, tomatos,potatos and...,its somewhat a watery food....we Iranians eat the watery food sopping bread in it and it is called " TERID" . whatever that remains (like grains and meat and... ) is then beaten and mixed with something like a hammer which is called "GHOOSHTKOOB" and this is how it is made ready.. :) :)

this phrase is used in different situation,I`l tell u two main situation:when someone is ugly another says,"goosh koobide",it can be humiliating.and another situation is when someone seems silly and stupid.

He means that she is Sexy but in an impolite way.