This is a sexualised and back-to-front version of a piggy back ride.

It involves the rider (typically a small boy) hopping on the big, long, hard willy of the other person (typically an authority figure such as a head teacher or priest) with their anus. The pair then ride around the room going "ooh, ooh, ooh" until the ridden penis reaches the point of climax. After dribbling out of the anus of the rider, the ejaculate (or "Brasso" as it is called during this sex act) is then used to polish the rider's botty.

The term originates from the Derek and Clive skit called "Sir" in which a fictional child describes getting a dicky back ride around the head teacher's study in lieu of punishment.
Sir: "I was going to punish you for being so naughty and looking at Wiggins' willy, but instead I'm going to take you for a dicky back ride around my study"

Boy (to friends later that day): "Oh that was a narrow squeak, I thought Sir was going to punish me!"
by Azbo The Great! July 18, 2018
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