From the back 

Sexual intercorse where the male is putting his penis in the female from the back side area into the coochie

Come here and let me hit it from the back

From the back by Tiffany November 9, 2003

knock the back out of

This is normally associated with sexual intercourse carried out at a rough and vigorous pace (most commonly doggy-style), although it can be associated with any activity where it is performed with gusto. This means that you did whatever it was you were doing with particular enthusiasm and/or speed

Good morning Casper. I had a cracking time knocking the back out of Lady Clementine Smyth last night

or

Gadzooks, I could certainly knock the back out of a few glasses of Moet this evening

knock the back out of by Cockles August 29, 2006

hamburger in the back pocket 

Euphemism used in reference to someone who is really, really, fat. Comes from the fact that fat people like cheeseburgers/hamburgers and might/would like to have one in their back pocket for eating at any time.

She used to be cute in highschool, but I heard she has a hamburger in her back pocket now.

The man with a hamburger in his back pocket ordered the buffet.

If you keep eating those chips, you're gonna end up with a hamburger in your back pocket!

A hamburger in the back pocket is the number one killer of Americans

hamburger in the back pocket by dontbesilly72 December 25, 2009

diamond in the back 

a characteristic of early model cadillacs used primarily by the urban community that was popularized in a classic song, "Be Thankful for What You Got" by one-hit wonder William Devaughn and has been covered and sampled many times over, most notebly in rap songs beginning in the early 90s.

Though you may not drive a great big Cadillac
Gangsta whitewalls
TV antennas in the back
You may not have a car at all
But remember brothers and sisters
You can still stand tall

Just be thankful for what you've got
Though you may not drive a great big Cadillac
Diamond in the back, sunroof top
Diggin' the scene
With a gangsta lean
Gangsta whitewalls
TV antennas in the back

diamond in the back by uncle sam November 5, 2004

down in the back 

having a sore back, usually a country term

Hey Elmer,you still down in the back?

down in the back by VictorM April 25, 2006

shit in the back seat 

a phrase referring to a female's big and phat ass, also known as Junk in the Trunk.

damn girl, you've got a bunch o' shit in yo back seat

have you seen my new baby mamma? she got some shit in the back seat!

shit in the back seat by The real D Sinjin III July 16, 2010

Jack in the Back 

1. Basically, a kid posing as a bamf who stands behind his/her crew and is afraid to take real action in a fight.
2. Someone who claims they can kick ass, and they chicken out when someone wants to go.

James: I saw Jason behind those punks fighting after-school today. What a whimp.
Rob: I know, such a jack in the back.

Jack in the Back by baddefinintionperson May 28, 2009