I will not let people tattoo the inside of my skin .
closed as unclear what you're asking by jimm101, Lawrence, Jason Bassford, sumelic, Scott Jan 6 at 2:30
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The sentence makes sense in that it is grammatically correct. As for making sense in a meaningful way, it does too, if you can think metaphorically, or even just imagine the gory situation in which someone would have access to the inside of your skin. We also have a saying, when someone "gets under your skin", it means that he or she is annoying you, making you very irritated or frustrated... In this way, your sentence does strike a nerve, it makes one think that you have been hurt so much by people, who have violated your mental/physical boundaries, but you are sticking up for yourself and not allowing them to hurt, or in this case, mark or draw on you any further.
It does make sense, it's just a slightly strange metaphor. I would think it means something along the lines of "I won't allow other people to permanently change how I feel about myself."
Sometimes when you're told bad things about yourself often enough, even if they're untrue, it becomes an instinctive way of thinking about yourself -- the words have been metaphorically tattooed on you, but not so other people can see them. They're only visible to you, yourself, as if they were tattooed on your mind rather than on your skin. I think that's what the author is saying, but I'd have to see the original context to know for sure.