A childhood game where you knock on someones door and then run away and hide and watch them come open it and see no one is there and laugh at how confused or annoyed they are!
Knock-a-door-run
by Del4sh June 19, 2013
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During anal sex, the person that is doing the penetrating and thrusting is the one that is doing the "knocking," and the anal opening is, obviously, referred to as the "back door."
When Eric and Amy are in bed, he's always knocking at the back door.
by Zeeky H. Bomb March 20, 2005
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n. when a man attempts anal sex without requesting verbal permission. Often involves either precursory acts such as foreplay (rimming, anal fingering) or preceding acts (spreading of ass checks, tapping head of penis on anus, pushing the tip of the penis onto the orifice without full insertion) to signal one's attempt at anal intercourse.
After doing it doggystyle with Jackie, I started knocking on the back door. She didn't object so I totally stuck it in her butt until she screamed.

Richard Johnson kept knocking on the backdoor last night in bed, but I told him to stop since I barely know him.
by calisp July 2, 2013
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The act of bored children knocking on a door, and reciting the alphabet, which ever letter they get to when the occupant opens the door, is the first letter of the Person they MUST ask for.

No real purpose but to impose serious embaressment on the knockee.
Kid 1: Who wants to play Knock-a-Door ABC?
Kid 2: ME!
*walks to a random door*
Kid 2: *Knock Knock* A B C D E F G H I J K *door opens*
Owner: Yes?
Kid 2: Hi is keith there please?
Owner: There is no keith that lives here.
by Sicked418 July 3, 2009
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A dirty way of saying surprise butt-sex.
1.Waffles: Hey Dwarfo, I'm gonna cum to your house and knock knock on the back door. If you don't answer, I'm gonna bang bang!

Dwarfo: Yeep! I hope it isn't too surprise!

2. What rapists say to little kids when they are gonna butt-rape them.
by Dr. Dirty August 15, 2008
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