20. Mariah Carey
Mimi is having none of it. She calls out Corden for his "act," looks like she'd rather be anywhere else and gives the disclaimer: "I'm not singing today, I've been up all night." The chanteuse relents, and lends her incredible pipes to join in on "Vision of Love" and other songs, and urges Corden to try his hand at his best New York accent. Hint: It's not great.