P.T.B.U. ratio
abbreviation for "Potential to Blow Up ratio", which is a scale ranging from 1 (low) to 10 (high), that rates the chances a currently hot girl will someday gain weight and become overly chubby and unattractive.

Key note:  One night hookups are exempt from the P.T.B.U ratio as the girl being rated is usually hot, and even though she is likely to blow up in the future, the aforementioned potential blow up will not effect her current hotness.
Tom: "Check out that chick over there... she is smoking hot."

Brent: "Dude, look her thick upper arms and those kankles, she's got a high P.T.B.U. ratio.

Tom: "Man, who says I'm proposing?  Bang it tonight, leave it tomorrow.