I’m not sure what the big story is here: the lawsuit or the emergence of the term “likejacking”. Facebook and the state of Washington are suing a company called Adscend. Likejacking happens when someone is lured into clicking a link in a Facebook ad which then marks the ad or Facebook page as something the user, in the parlance of Facebook, Likes.
This is what the plaintiffs are saying Adscend was doing:

One of these alleged Facebook scams includes a Facebook post that offers the promise of a salacious video of an ex-girlfriend. When a user clicks on the post, a window opens seeking “Age Verification” that users need to click on to proceed. But it’s a trick. When users click on the link, they link gets shared in their news feed. And then users are also redirected to an Adscend advertiser site, for which the company receives money.

One could argue that if you’re dense enough to believe that there’s an actual salacious video at the end of that link, you deserve all the spam that’s coming to you. Washington Attorney General Rob McKenna says it’s not clear whether the advertisers working with Adscend are aware of how they’re getting this new traffic.