The infamous "Snake Charmer" puzzle on the British version (November 1994), in which the partly-revealed animation appeared to show Mr. Chips engaging in an activity associated with 14-year-old boys. Cue everyone in the studio being reduced to fits of laughter. It really didn't help that the squares that were picked just happened to be the ones revealing Mr. Chips' rather unfortunately-shaped head and the head of the snake (which gave rise to the alternative thought that Mr. Chips might be jacking off with the snake. Or jacking the snake off).
One of the most grotesque catchphrases the show has featured was turned into one of these. The puzzle showed three young army men being gunned down, followed by an elderly trooper repeatedly dodging the bullets. Following the initial laughter at the animation of him dancing around the screen and a few guesses, one of the contestants suggested Firing Blanks; the studio fell about laughing. (The correct answer was Old Soldiers Never Die.)
One outtake from the original TVS run had the contestants trying to incorrectly solve a catchphrase. After they both tried, Roy gives them the answer, but instead of giving them the correct answer (Blue Heaven), he instead tells them the answer is 'Columbo'. The look on his face afterwards is just priceless.