I believe that Heinlein "coined" the acronym, but the phrasing comes from Friedman (except, perhaps, the "ain't") and the concept including the phrase "free lunch" seems to date back to the California Gold Rush, though it was probably much more literal back then.

However, Doug seems to be a fan of SF lit, so I bet he initially picked it up from Heinlein. (Though I'd personally argue the literary merit of Heinlein.)