To make someone very happy: “You won first prize? Now that really makes my day!” The saying dates to the beginning of the twentieth century, but it gained popularity with its use by Clint Eastwood in the Dirty Harry movies and, later, by President Ronald Reagan.
Go ahead and do what you appear to threaten, so that I can trounce you and have a successful day: ''Make my day'' is much used in the New York subway system, where life is raw and tempers are short
[1971+; popularized by the movie star Clint Eastwood, who used the line in one of his Dirty Harry police thrillers]