Nice try evil doppelgänger, nice try.
If I suddenly became a competent adult, I think it might tip people off.
If I ate something in silence, my partner would likely notice something was off immediately. The sound of even my own chewing (mouth closed, ofc) triggers my misophonia
Nice try AI.
Personally, I never have my radio on in the car and I near-always back into parking slots.
Don’t answer this you fools!
Nice try, shapeshifting doppelganger. I already have one evil twin, thanks.
I am unable to speak using contractions.
Well this obviously depends on how well informed my impostor is. But I would say my choice of sushi or breakfast would be among things that could out the doppelganger. Also my choice of drinks, the drink would probably out the doppelganger faster than the food.
Food related patterns would be pretty strong indicators for me as well, I think.
I only eat after 4pm (sometimes only from 6-10 or so) and people comment when I actually eat earlier than that, especially breakfast. I almost never use condiments or salt (I’m on a very low sodium diet and have been most of my life; I don’t use salt outside of baking, and that’s half salt). Give my dopple unsalted fries and you’ll know right away.
Drinks would work well for me as well - coffee made a very specific way, or room temp water, mostly (I actively dislike cold and hot water).
My Kiwi accent (despite not being in New Zealand), my abnormally dark irises, my teeth (nothing particularly unusual except a few have an odd shape), my honeymoon rhinitis, my distinct snoring when I sleep, my semi-snorty laugh, my uncanny ability to quote my favorite media, my asexuality (supposing someone were to try to tempt me in ways that would tempt anyone else), my talent in cryptography (or rather certain kinds), my art style, and how I elaborately express myself all come to mind.
Following your example, I never throw on a playlist or let my streaming app generate one. Albums all the way.