contradict something said before, talk or act in the opposite way Usually he doesn`t care if he disturbs his neighbors at midnight but now that he has to get up early in the morning he is whistling a different tune.
SING (WHISTLE) A DIFFERENT TUNE
Meaning of SING (WHISTLE) A DIFFERENT TUNE in English
English idioms vocab. Словарь английских идиом и выражений. 2012