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
Gadzooks, I could certainly knock the back out of a few glasses of Moet this evening
To be incredibly enthusiastic about something, almost to the point of sexual arousal. Used if an aquaintance constantly bleats on about a particular person, place or thing. Normally accompanied by the lifting of the arm gesture whilst slightly bent at the elbow
Golly, Tarquin has an absolute full-bar for playing polo on a Sunday
A crease or gash in the male genitalia of astounding girth.
Girl 1: Blowing John hasn't been the same since he got that assassin's crease.
Girl 2: What do you mean?
Girl 1: There's a huge crease in his dick from wearing those tight jeans.
Girl 2: Oh, my boy has one too, he got ran over by a snowboarder!