Colleen Hoover. Photo: John Nacion/Variety via Getty Images “This may be either a new rock bottom for me or the best thing to ever come out of my brain,” Colleen Hoover began in an Instagram Story on March 18. What she presented was not a forthcoming romance novel — the genre upon which her best-seller fame is built — but the idea of freezing Diet Pepsi in an ice-cube tray so that she can cool her Diet Pepsi with, well, more Diet Pepsi. This isn’t an especially original idea, as “coffee ice