Glowleaf

 

Check your top 20 competitors. (you have an eye on your competition, right?)

Mark those who are foolish enough to run adsense (never, I repeat never, use adsense on your main site)

Target the campaign only for that site. Make your ad, show on your top competitor’s site only.

Bid 20-25 $ on it. Don’t worry, the clicks will not be that many.

If you want to take it a step further, create 2 or 3 adwords accounts, and flood his adspace. Make your ad say, “this site sucks, but here you can find a much better one”. Or, if you want to be less aggressive, “insert-site-name a scam? Get informed before you buy. Find out more here” and link to a fake review on your site.