The gag, by deadpan Canadian comic Stewart Francis, picked up one-fifth of the votes in a poll of comedy fans organised by British TV channel Dave.
The winning joke – “You know who really gives kids a bad name? Posh and Becks” – comes from Francis’s current show, Return of the Lumberjacks.
The names of the couple’s children are Brooklyn, Romeo, Cruz and Harper Seven.
The competition, which has been running for five years, enlisted the help of 10 comedy critics to draw up a shortlist of gags.
The list was then put before 3,000 comedy fans.
Francis said of is win: “1969 West Mall Soccer Association’s Most Valuable Player, and now this… thank you, Dave.”
He also had another entry in the top 10 jokes: “I saw a documentary on how ships are kept together. Riveting.”
Francis held off tough competition from one-liner legend Tim Vine, who holds the Guinness World Record for the most jokes told in an hour – 499.
Steve North, general manager of Dave, said: “As Dave’s Funniest Joke of the Fringe celebrates its fifth anniversary it’s great to see how the top 10 get wittier and sharper every year.
“Stewart Francis is a very worthy winner and with his droll quip has proved himself to be king of the one-liners.”