A formidable man who says what he means, expects others to do the same and is disinclined to tolerate discourteous behavior from others.
The term first entered the popular lexicon following the release of the film "Cadillac Man". In the film, the character of Larry (played by Tim Robbins) is holding a group of people hostage. He releases some of the hostages, but instructs them to tell the police that "I'm a no-shit guy." The hostages then run from the building one by one, screaming "He's a no-shit guy!"
"Jimmy's a no-shit guy, he told me he'd be here, and so he'll be here."
"Whatever you promised Mike, you'd better deliver. He's a no-shit guy."