From the WWII era meaning Section 8, a category of military discharge. Service members were deemed "Section 8" if they were mentally unfit for service. This included being found guilty for sexualal perversion. In modern times it is used to describe a soldier or piece of equipment that doesn't perform or present to military standard.
DS Slaughter- "PVT Snuffy, you failed to shoot at least one of the 40 targets with your rifle. Why are you so 8 up?"
PVT Snuffy- "Drill Seregent, I'm not 8 up, it's my rifle. It has been jamming and double feeding all day."
DS Slaughter- "You are still 8 up for failing to conduct proper maintenance of your weapon PVT! Your weapon will function properly of it is clean and lubricated!"