I use Google AdSense, the ads at the top of the page here, to generate a small income from the site. It pays about half my hosting costs each year.
One of the entirely reasonable rules is that you don’t click on ads on your own site. The annoying thing is when you click on a window to bring it to the front, and it happens to be your own website, and you happen to hit one of the ads, as I just did.
Google are fine about this, provided you report it straight away, but discovering how, is a little trickier.
It was relatively hard to find the answer to this, so I’m adding it here in case there’s a next time. The URL to visit to report accidentally clicking on AdSense ads on your own pages is: https://www.google.com/adsense/support/bin/request.py?contact=invalid_clicks_contact.