According to email from Jonathan Ferro, of the top twenty Google hits for "not in my vocabulary", only one (in blue below) is not a linguification snowclone:
1. dieting 2. failure 3. lasting relationships 4. worry 5. universal design 6. abort 7. boredom 8. compromise 9. enough 10. lame duck 11. fear 12. exploit 13. sour mix 14. guilt 15. early retirement, mortgage paid in full, travel around the world 16. drop pearl earrings 17. cicadas 18. nice 19. fail 20. inactivity
Jonathan adds that "I also looked into 'not in my dictionary', but only two of the top ten are genuine linguifications, so I didn't dig further".
Looking in LION, I found Frederick Thomas, Clinton Bradshaw; or, The Adventures of a Lawyer, Volume 2 (1835):
If Talbot were poor, he might do something; but now, bah! he will be spurred into an occasional feeble effort, and fail. And his wealth will give him all the leisure to canker and fester over it. But I — the stern necessity is on me to labour — to do head work — and if the sweat of the brain is like other sweat, a plebeian offering to the goddess industry, may be I may pluck, in my rough road, a certain leaf or two, and hide the sweltering stain upon my brow, as Cæsar hid his baldness. `Impossible,' said Mirabeau — `that word is not in my vocabulary,' nor shall it be in mine."
And this from Charles Smith, The Wild Youth: a Comedy for Digestion (1800) [translation of a play by August von Kotzebue]:
Lisette: Patience! patience! Frederick: This word is not in my dictionary. Lisette: Then write it in it. Keep your tender letter. I shall tell her, that a handsome young gentleman, with a pair of large wild eyes, has resolved to love her eternally. Not so?
Alejandro Satz wrote to remind us of the famous Napoleon quote (which may have been inspired by Mirabeau or by an older usage inspiring both):
'Impossible' n'est pas français. [Letter to General Lemarois (9 July 1813)]
Alejandro also cited a widely-used variant English version of a similar sentiment, also attributed to Napoleon, whose source is less clear:
Posted by Mark Liberman at July 9, 2006 08:31 AMImpossible is a word found only in the dictionary of fools.