Send Slayerduck the details on rule34 mail including:
What you where clicking on when you got the popup.
When roughly this occurred.
What location roughly, since ads change depending on location.
What browser.
What Operating system.
A description or screenshot of the popup would be the most help (just upload it to one of the many free image hosts and send him the link, it's important we know what it looks like when we report it to our ad host.
I think that's all he needs.