"JODY" was the guy that stayed home in the US. Slept in your bed. Drove your car. Ate your Mom's home cookin'. Slept with your girl. Rode your motorcycle. Jody is a universal name for either a draft dodger or a 4F (not fit for the military).
Through basic combat training (BCT) and advanced individual training (AIT), we marched to songs that told stories of what "Jody" was doing while we were in the service.
Just for the record, for you potential "Jody's" still out there, when we got home we kicked their A$$!