ADDED: The bracketed "heyday" above replaces the Daily Caller's "hay day." Did you think someone's "heyday" had something to do with hay? Were you picturing something like this:
No! You are wrong:
late 16c., alteration of heyda (1520s), exclamation of playfulness or surprise, something like Mod.Eng. hurrah, apparently an extended form of M.E. interjection hey or hei (see hey). Modern sense of "stage of greatest vigor" first recorded 1751, which altered the spelling on model of day, with which this word apparently has no etymological connection.