Arm Theory
The scientific theory that allows a male to determine a female's figure and/or bodytype based solely on the size, shape, and density of her arm. The male is able to determine whether she is fit, skinny, fat, or even skinny fat based on a single glance.
If her arm is super thick but she still has a pretty face then Arm Theory states that she is better labeled as "fat" and not as "pretty."
upper arm theory
The circumference of a female's upper arm can determine how much she will weigh in the future. A larger circumference predicts a woman will gain weight uncontrollably as she ages, while a smaller circumference predicts that she will keep her petite figure without much effort.
"Damn dude, the upper arm theory predicts your bitch will be fat by the time she is 30"