Hi, Monica!
You've probably already noticed, but when you go to your User CP and see the subscriptions listed, there is an option to "Unsubscribe" that you can click on under the title of the post. It will take it off your subscription list. That's what I do when I feel I have blethered enough about a post!
But, perhaps you are asking how to prevent it to be on the subscription list in the first place? That one I don't know.

Kathryn