Said about a sexually appealing woman, with whom you would be very eager to have sex.
To explain the metaphor: you may be a little too vigorous, and push your penis all the way through her, hence, knocking the back out of her... Obviously not physically possible, but a good, although rather crude, metaphor
Guy A: Phwoar, Check her out, what a stunner!
Guy B: God yeah, I'd knock the back out of that!
May I have an order of regular degular buttermilk pancakes? Without all the added jazz? Hold the blueberry smiley face, strawberry glaze, chocolate chips and whipped cream.
Usually a male who likes to encourage weight gain in his partner through the consumption of food. Feeders differ from FAs... whilst an FA is attracted to big girls, a feeder gets turned on by making a thin girl fat....or a big girl even bigger.