When someone rates the looks of the person they're having sex with (1-10), higher than most people would say. To make it seem like they don't bang ugly people.
A 1-10 scale for rating women. This scale is usally 3 or more points higher then what most people would rate the same girl.
"That girl is cute I'd say she's a 6. A 9 all day on the Joubert scale."
"I finally met the girl Jay said was an 8, there's no way . He must be using the Joubert Scale! She's barely a 5."