Something awful happens. The lovers finally break up, the heroes get captured, a beloved character dies, The Bad Guy Wins...and after the smoke clears, one of the characters suddenly remembers that today is their birthday. Used to heighten the dramatic irony of something so tragic happening on what is supposed to be a happy day, and symbolizing how the character(s) will never be the same. Compare/Contrast Ironic Birthday, which is when the bad thing in question has to be kept a secret, and the character in question doesn't remember his/her own birthday until the party.