Since most advertisers are bidding CPC (cost-per-click) they only pay when the ad is clicked vs. when the ad is shown. If they are buying impressions then they pay whenever the ad is shown.
If you want to cause financial damage to a company the best way do so is to actually click the ad, so Google will bill them for it, then close the page after 10 seconds. That way it will register a bounce. The higher the bounce rate is the less important/relevant a website is.
That's about the most damage you can do.
If that's too much effort then you can also click the little X on the upper right of the ad. When you do so the ad will disappear and it will say, "Ad Closed By Google". Then it offers the option, "Stop Seeing This Ad". If you click that, presto you won't ever see it again.