BANG! Flag Guns are often used as a practical joke when someone intends to shoot a person, but is unable to when it turns out their gun is fake and doesn't shoot actual bullets but only a silly little flag instead. The same gag is also used at times when a person attempts suicide with the same outcome. The implied murder and/or suicide makes this "joke" really a matter of Black Comedy, despite the otherwise harmless nature of this gag gun.
DC Comics' Joker has certainly made the BANG! Flag Gun a staple of his villainous repertoire, but with it often actually being lethal by - for example - having the BANG! flag shoot out of the gun and stab its victim like a spear. Writer Len Wein, penciler Walter Simonson and inker Dick Giordano first debuted this version of Joker's BANG! Flag Gun in March 1980's Batman #321: "Dreadful Birthday, Dear Joker...!"