The BIG square fat bloated arse that dieting women have. Caused by the chemical sweetener in their diet croak drink that they are totally addicted to.
The methanol content of aspartame converts to formic acid and formaldehyde once inside their body, the formaldehyde then attaches to fat cells making it impossible for the body to burn off that fat. Result is the fat stays, the body gets fatter, it all ends up around the arse.
Bloke one: "Hey, have you seen the size of you're wifes back end?"
Bloke two "Yup, can't really miss that aspartame arse, she's on a diet".