Sorry I took so long to get this answered, I didn't know where this page was until I stumbled on it by accident. It used to mean Just another ****ing Officer when I was in the infantry (I was enlisted). But now it's Just another ****ing Operator, I fly unmanned aircraft for the Army, now. It seems it's a popular acronym with many different uses.
Hey JAFO, know you are on leave from service. Noticed your screen name. Are you a scout? We used to use that term for observers and scouts in back of Bradley. JAFO(Just Another ****ing Observer).
Antway, enjoy your time off.