Joe
Of course, you can have a cup of coffee. However, coffee is not a stimulating beverage in the military. It’s a phrase for service members, similar to another well-known one, grunt. Joe is typically a low-ranking soldier. Private Joe Snuffy is a nickname for the average soldier. It’s hardly flattering.
PX Ranger
You must first understand what the PX is. Military bases have a general store, which is officially known as the Post Exchange. Everything from military equipment to candy snacks is available. A PX ranger is a soldier who has over-equipped themselves with PX equipment. The inference is that they’ve probably overburdened themselves with goods they don’t actually need.