be not whistling Dixie

be not whistling Dixie

slang To have a realistic or honest view of something; to be speaking truthfully. "Dixie" was an anthem of the Confederacy, the losing side of the US Civil War. Primarily heard in US. It sounds like they really are laying people off in January. You weren't just whistling Dixie, Bob! They've threatened to fire their missiles on civilians; I don't think they're whistling Dixie.
See also: Dixie, not, whistle