When The Flash brought back Michael Keaton for another turn as the Dark Knight, it made sure to make some jokes in honor of his tenure as the character. And one of its many was a callback to Bruce Wayne's line in Batman (1989) about getting "nuts." Becoming an iconic phrase, many fans were excited to hear Keaton say it again in The Flash's trailers and in the film itself.
Source：https://www.cbr.com/the-lego-batman-movie-outdid-the-flash-joke/
