"A fool's tongue is long enough to cut his own throat." -- Bruce Waltke, The Book of Proverbs: Chapters 1-15 (2004), p.102.
Waltke is summarizing a bunch of statements from Proverbs on wise use of words, and right in the middle of his summaries (usually followed by a bunch of verse references) he has this one proverb of his own (with no verse references). I guess when you write a 1200+ page commentary on the book of Proverbs, you begin to think in proverbial form. I have to say that it's quite an image.
There's a slightly cheesy but still funny passage two pages later that doesn't fit the same description, but I thought I'd include it while I'm quoting Waltke:
As these means of obtaining wealth show, it is a matter of character, not of method. Proverbs is a "how to be book," not a "how to" book. Solomon is a better theologian than Frank Sinatra: Sinatra sang, "Do-be, do-be, do"; Solomon sings, "Be-do; be-do; be."