Noun: Common office slang used by professional business men when referring to taking a "duke". A blue devil can be any size or texture of poop. Any man's duke is worthy of being called a blue devil.
The term (already common in the Midwest) is becoming common because it gives men the freedom to publicly discuss their bowel movements in the workspace without being reported to Human Resources.
Chris was late to his meeting because he had to take a last-minute blue devil. Too much coffee will do that to you.