A colloquial, quasi-humorous term for someone who is unsure of their location in space and may even be unclear about the left versus right sides of their own body. As psychological testing suggests, women may tend on average to have better liguistic skills than men, while men, in general, might have better orientation in space, so a man who is "directionally challenged" may be seen as less masculine by his peers. If a lifelong trait, it may represent a form of Minimal Brain Damage (MBD) related to Dyslexia or Attention Deficit Disorder (ADD); but if it occurs for the first time in a middle-aged or older person, it might herald a future dementia, such as Alzheimer's Disease (AD).
One reason (aside from instilling discipline) that the armed forces emphasize close-order drill in the training of recruits is to weed out the directionally challenged as someone who is such--"S'matter? Doncha know yer left from yer right? You directionally challenged or sompin'?"--will tend to do poorly on the battlefield and may even jeopardize the lives of his or her fellow soldiers, sailors, or fellow fliers.