Google added a '+1' feature to promote certain results. Once a few people upvote a result, it's universally seen closer to the top of the results page.
The Google Help pages include a way to report some inappropriate or totally irrelevant results but not to '-1' them.
How do I downvote a result, if it's not useful to the subject (while still a bit relevant)?
Update. This question is about results when not logged in -- which is what everybody would see. Hiding results just for me isn't the matter.:)