I've expressed my dissatisfaction with the phrase "I'm normal" and the way it's used as an acceptable method for joking self-deprication before, but I feel like retreading that a little bit. because I feel like it just sort of keeps getting parroted without any critical thought.
the way it feels to me is that the "tongue in cheek" behavior of stating "I'm normal" when presented with unusual stimulus that you feel strongly about (whether it be a hyperfixation, a specific kink, or something else) is a method of deflection. by choosing this response, you're denying yourself the capacity to fully indulge. "I'm normal," you say, in jest, fully knowing that you're not normal, but choosing to deny yourself the option to fully engage with the particular topic being presented.
the other part of it that sticks in my craw is how the phrase acts to spread shame. someone saying it might have full confidence in themselves, sure; but in saying it, in denying themselves full engagement with the particular source of enjoyment, they're creating this sense that the source is shameful. "I'm normal," you say, and people may understand that you're not normal about the subject, but the perspective is still created that interest in that thing isn't acceptable to allow yourself to associate with it. it closes it off. makes it unacceptable to openly discuss. sure, you like it, but you're normal. normal people can't talk about that.
this is all to say that adherence to this joke is holding people back from being their most honest and genuine selves. I would love to see this phrase scrubbed from furry spaces someday, and replaced with a culture that just lets people be open to themselves and their friends.