Projection is a paranoid ego defense mechanism in which someone recognizes his or her denied characteristics in someone else. Related is projective identification, in which characteristics acknowledged in oneself are recognized in another. Projection is generally thought to be pathological because an individual's psychological makeup is internally denied and externalized onto his or her environment instead.
This leads the discussion to a well-known example of trait externalization: yo' momma jokes. E.g.: "Yo' momma's so fat she keeps the Earth anchored in orbit."
In this case, one can postulate that the joke's originator may subconsciously believe himself or herself to be fat, and so he or she projects his or her feelings of overadequacy onto the interlocutors' mother, thus denying himself or herself the awareness needed to get to the gym.
Another example is, "Yo' momma's so fat she got arrested at the airport for carrying ten pounds of crack." In addition to the feelings of overadequacy exhibited in the previous example, the teller of this joke seems to be infatuated with drug culture. The careful reader, however, would be advised not to conclude that this jokester will end up on the streets, selling his or her plasma for his or her next chemically induced euphoria.
A surface review of the history of yo' momma jokes reveals that they orignated in male African-American urban youth culture. However, because of the abundance of yo' momma jokes referring to obese and disfigured maternal personnages, a more apt conclusion is that yo' momma jokes originated among male white middle-aged middle-class culture. It would seem these average, red-blooded American Joes were not only projecting their own overadequacies onto other people's mothers but also slyly using inner city youth culture as a convenient skapegoat. Not only is this sneaky because it seems implausible to the layperson; but it is, moreover, quite morally reprehensible. That suburbia has gotten away with this conspiracy until now is a clear sign of the downfall of American society.