Proper use of "vernacular"

Solution 1:

This is an incorrect use of vernacular; it really should be vocabulary. The reason why this is incorrect is that vernacular refers to the vocabulary of common words shared by a group of people. You cannot add new words to it at the drop of a hat.

It may be misleading to say my vernacular; it is important to realize that this means the vernacular you share, not the corpus of words you personally ordinarily use. Your personal word list is called your vocabulary.

You can see the incorrect way in use by googling "add it to my vernacular" (47 results), and the correct way by googling "add it to my vocabulary" (266).

Solution 2:

This is not the correct use. You're assuming that you can add the word "Curmudgeons" among a group of people, not just yourself.

Solution 3:

A vernacular is the language spoken by a certain group or people living in a certain area (see OALD and CALD). Use in your example sentence is inappropriate unless it is used humorously or metaphorically.