If a barista or anyone else was truly trying to shame me for drinking decaf, I think I’d find another place for coffee. Back before the virus, when I worked in an office, half (or more) of the pleasure of going for coffee was friendly human contact. Or, bonus points if you want to gently correct the person; as I said above I mess stuff up all the time and appreciate when a friend makes me see when I’ve been unintentionally rude.
It turns the conversation upside down and makes the other person sound like a junkie.
Alcohol is thus not essential for the feeling from drinking a good beer: MAO-B inhibition alone tends to produce euphoria.
Isn’t it interesting that all our legal drugs contain MAOIs? Coffee, tobacco, tea, beer, wine, even energy drinks...
In your case, both the taste and effects are produced by certain monoamine oxidase inhibitors (Harmala alkaloids) created in pyrolysis of L-tryptophan during the roasting and brewing of coffee.