Karl Kicks His Height
As a kid, Karl once "kicked his height" per his father's challenge. One summer's day in the era where Kung Fu was popular, Karl was outdoors playing around punching a tree. Mr Pilkington said he bet Karl couldn't kick his own height (around five feet at the time), and Karl did it, but, whilst inviting his Dad to look, he didn't put his foot down. The result was that he landed on his back on the concrete floor. Karl thinks this is the root cause of his back troubles.
Quotes
Karl: "I was that chuffed that I got that high, that I didn't think of putting me leg back down again"
Steve: "'I kicked me height' - it's not a well-known phrase! You can't just go 'I kicked me height'!"
Ricky: "What sort of a kid he must've been!"
Ricky: "The other kids must've been saying 'get Karl Pilkington to try and kick his height, I bet he falls on his arse like a fucking penguin!'"