Akashingō minna de watareba kowakunai: if everyone crosses on a red light together, it is not scary. The line began as a dark gag by the comedy duo Two Beat, Beat Takeshi and Beat Kiyoshi. It was printed in a book of their jokes in 1980.
Japanese Wikipedia explains the phrase this way. Even something that is forbidden can be done without psychological resistance when it is done as a group. The phrase entered the eighth edition of the dictionary Sanseidō Kokugo Jiten in 2021.