A person who is a expert of determining women's breast sizes. They also have a ability of telling if they are real, fake and/or if they are using a stuffed/pushed-up bra/braless, all simply by looking, and WITH the woman being fully clothed.
Bob: Wow, Judy really loves them think sweaters. I wonder what her bra size is.
Steve: *looks* She a 38C. And they're real. went with a brassier today. Nice.
Bob: How the hell do you know that ?
Steve: I've got the mad skills man. I'm a Boobieologist