Similar to the imaginary and often sought after "dislike" button on facebook, "minus 1" or "-1" is a way for a user of Google+ to express dislike for an item in the social networking service. Due to the fact that there is no "-1" button to counter Google+'s "+1" button, this contempt is usually expressed in the form of a written comment on someone's post or status.
Person 1 posts: The new hugemongous
size cup at the coffee shop is totes
Person 2 comments: minus 1