Sometimes, while praying, I'll quote Scripture to the best of my abilities. It helps if I have the Scripture I'm thinking of in front of me, but obviously that's not always the case. I must quote from memory. As I sat there praying recently, I quoted Isaiah 40:31, of course from memory. The trouble is, although this is one of my favorite verses, it's easy for me to mess it up when it's not in front of me.
In the KJV, Isaiah 40:31 reads "But they that wait upon the Lord shall renew their strength; they shall mount up with wings as eagles; they shall run, and not be weary; and they shall walk, and not faint." When quoting from memory, I often forget the bit about the eagle, swap "run" and "walk", or both. Now, in my quoting of it, the context and meaning never change. It's always about the blessings that will one day come from trusting in the Lord. A renewed strength, which in Heaven will never deplete.
But the kind of mix-ups I make in my off-script quoting are exactly the kind of mix-ups KJVOnlyists often criticise other translations for. In the most extreme KJVOnly groups, the importance of "every word" is emphasised to the point where if "Christ Jesus" becomes "Jesus Christ", or vice versa, even that is seen as a bad translation, and a trick by the devil to dissuade Christians from relying entirely on the perfect word of God as found only in the KJV.
Now, no matter how much we study Scripture, the human memory will never be perfect. Because of this, even the most committed, hardcore, sincere KJVOnlyist will, at least on occasion, mess up their citations. Therefore, in order to be consistent, they should never quote the KJV except when reading from the KJV itself, lest they goof, and do what, in their philosophy, Satan himself apparently really wants them to do.
Now, perhaps you think I'm being too extreme here. And in one sense, you're right. However, KJVOnlyism itself is an extreme view, and I am only addressing the most extreme elements of it. I am addressing the kind of person who genuinely does think those who do not practically worship the KJV are heretics who should be divided from, like the KJVOnlyist who, after losing a debate with me, cited Titus 3:10 as a reason to never talk to me again. But of course there are more rational Christians who would describe themselves as KJVOnly, not because they are that extreme, but because they think there is something particularly special about the KJV.
To be clear, therefore, I am not pointing out an inconsistency in the latter group's thinking. Rather, I am pointing out an inconsistency in the more extreme line of thought. If you think it is heretical to use a Bible that is not the KJV because these Bibles are not exactly like the KJV, which is the core of almost every KJVOnly argument, then to quote the KJV from memory risks your very mouth becoming as filthy as the dreaded NIV.
If a KJVOnlyist denies the significance of messing up a memory verse, they must automatically deny the significance of the KJV, simply because none of their charges against other translations stick, and for the same reason. No matter which way you cut the cake, there is nothing more radically different in more modern, reputable translations than a failed memory quote. If, by contrast, they want to argue that wording matters more than meaning, they should be as angry about a failed memory quote as about one of those "new age" translations they hate so much.
Thus, if a KJVOnlyist is ever caught risking a memory quote, and especially if their memory messes up and they quote a verse differently to how it appears in the KJV, they are acting inconsistently with their view. Yet, they do this all the time, even when defending KJVOnlyism. So, what does that say about the confidence they have in their view? What it tells me is they have too large a plank in their eye to even perceive the alleged speck in the eyes of Christians who, for whatever reason, do not have an exclusive preference for the KJV.