I have a "very socially competent mode of speaking and acting" that I can dip into when needed. I think you're doing a disservice to yourself by delineating between what "is fake" and "what is real".
It would perhaps be more useful to differentiate different modes of interaction as "personal/intimate" and "personal/non-intimate".
I put the "personal" in there to empathize that you're still you when you're doing these "things", and dipping into this type of performance doesn't mean it comes at the expense of your own aesthetic or considerations.
I think a lot of very socially shy people - like I am, at my core - do the mistake of romanticizing this "at-baseline-personality" to the expense of never trying to see if they can fit into any other mode of being.
I also think that, as a result of romanticizing your natural state of being quiet, introspective, passive (or whatever), a lot of people make the further mistake of assuming that people who aren't performing like you, in the moment, are dumb, or lacking interior complexity in some way.
My baseline personality is extremely introverted, high-anxiety, and with a nearly inert interest in trying anything new. Throughout my late 20's and early 30's, I learnt a baseline type of social patter that I didn't have before, and it was very transformative for me.
It made me feel like less of a failure - in general - but it also made me feel dumb for all the years throughout my life that I made an unnecessary differentiation between "people who talk a lot" and "people who are quiet" as markers for "dumb" and "smart" (respectively).
My point - if I have a point; I'm chilling and drinking wine - is that "modes of being" in the context of contemporary society should not make you feel dumb, in any way. What these markers are, is signifiers of difference, and that's all that they are.
How you react to these signifiers is really up to you. I think the way most people react to them, is very juvenile (sorting people into A and B groups, rather than allowing for the reality that any individual contain a multitude of "ways of being", and that social expression tends to be heavily curated and self-regulated/policed).
The TLDR of this post is that "being", in a social context, and in the sense of being perceived by others, tends to hinge on expectations, and that whatever group of society you think of as smart, or sophisticated or cool, is also ruled by similar constraints.
So, given that we have all these - mostly arbitrary - ideas of how to be, what makes the most sense? To play exactly within expectations, or let your brain dip into a new mode of being (and perhaps gain a more profound understanding with other people, in doing so)?
Super-TLDR: A lot of my internalized sense of otherness has been alleviated by me learning, on my own, in my early 30's, how to talk to strangers in a way that is warm, friendly and inviting. In doing so, I have made use of "silly fake words, phrases and inflection". But the sum total of that decision that I made a few years ago, was that I have become more (I think) empathetic, and internally beautiful than I could ever be if I were just to continue being an unsocial, human-spider being, who spent a needless amount of time feeling the need to - after the fact - act out small interactions with cashiers, looking for reasons that weren't there, to continue being as odd as I were.
Ultra-TLDR: The human brain is extraordinary, and we sometimes forget that, because we're so enamored with a self-generated idea of ourself. The times I've experiences a "weak node" in my consciousness - in the sense that it could be a branching path to something other than what currently is - has been extraordinarily beautiful to me.