The blog Live at the Witch Trials proposes a method for harming the search engine rankings of any companies you feel may be deserving. To abbreviate:

• Look through your target websites terms and conditions to find a clause that prohibits linking. Ryanair’s site has the following T&C:
  “Links to this website. You may not establish and/or operate links to this website without the prior written consent of Ryanair. Such consent may be withdrawn at any time at Ryanair’s own discretion.”
• Search for all the websites that do link to them anyway.
• Find contact information for those sites and send them strongly worded cease and desist notices that look official, but make no false claims.

This should have a pretty big impact on how important search engines feel your targets site is, and they’ll soon start to drop in the rankings accordingly.

Fun!