not know one's ass from one's elbow

:  to perceive directly :  have direct cognition of

:  to have understanding of

:  to recognize the nature of :  discern

:  knowledge

:  any of several hardy gregarious (see gregarious 1a) African or Asian perissodactyl mammals (genus Equus) smaller than the horse and having long ears

:  an African mammal (E. asinus) that is the ancestor of the donkey

:  a stupid, obstinate, or perverse person

:  buttocks

:  anus

: used as a postpositive intensive especially with words of derogatory implication

:  the joint of the human arm

:  a corresponding joint in the anterior limb of a lower vertebrate

:  something (such as macaroni or an angular pipe fitting) resembling an elbow

:  to push with the elbow :  jostle

:  to shove aside by pushing with or as if with the elbow

:  to force (one's way) by pushing with or as if with the elbow