The idea comes from the practice when
two girls go down on a guy. Since both girls cannot pleasure the head of the penis at the same time, one girl is forced to take
the shaft of the dick. Hence, the word shaft or shafted referring to being screwed into a lesser deal or something not as desired.
man, i really got
the shaft with these english groups.
Damn, you really got shafted when
Leslie left you for
Stan.