Contrived is a turn off to me. If someone says: "talk dirty to me," i cannot produce it on demand, and i would not want to put Him in that position either. i think maybe for some, telling a person: "talk dirty to me" is sort of like telling them it's okay, giving them permission.
i think 'talking dirty' is really intimate, it's saying stuff out loud that maybe one is thinking, but afraid to say. To me, that's what makes 'real' "dirty talk" so powerful, because you're sharing a scary need/desire, that when it's mutual, can help cement a deep, intimate connection/bond.
i have a long time fantasy where i have a connection with a Man and He knows He can use me anytime He wants to cum or piss in me. i'm sure just reading that sounds "dirty" to a lot of people. But if it's a mutual desire? i imagine waking up in the middle of the night to the feel of Him pressing His cock into me. As i wake, He whispers in my ear: "Take my piss, i know you need it." It's "talking dirty," but it's also deeply intimate for both of us because we both want it and know it's true.
i think "talking dirty" is very personal, i don't see it as working generically.