I heard about a case recently that made me think about all the people, especially the small artists, who get angry when they find a (potential) infringement and go onto social media to rip the, um, lets just call em badguys. Short answer is, even though you think it will help or at least make you feel better, youd be wrong. In fact, you could be inviting a lawsuit filed by the badguys.
Heres the very generalized skinny on the case (because really, unless you are a geeky lawyer like me, it is a dull read). One business (a kind of review site) publicly published that another business was a copyright infringer and that it had adult movies on its site. That arguably hurt the second business, so that onesued the first for various things that roughly amount to the business version of defamation. The court threw out that suit, under the California Anti-SLAPP law, which which exists so that people cant use the judicial system as a way to silence legitimate speech.
Okay, you may be thinking, the allegedly name-calling business didnt lose so whats the big deal? The big deal was that it wasnt a slam-dunk. Proving that the publication of something (potentially) defamatory was protected speech and that the lawsuit had to be dismissed under Anti-SLAPP wasnt easy. Similar cases have not been dismissed and you don’t want to be one of those.
Lots of people think they have a First Amendment right to say whatever they want about whomever they want. Trouble is, that isnt so. There are limits. You cant defame someone (or a business), for example. And if someone sues you in California for what you said, then, to get the case kicked out, you are going to have to prove that your speech was (1) an exercise of your First Amendment free speech right and (2) that it was made in connection with a public issue or an issue of public interest. Thats a pretty high bar to get over. In fact, youre going to have to show that the subject person (business) was famous/a pubic figure, or that the subject matter of the speech is of great interest to enoughpeople not affected by the case, or that the topic was of general widespread interest. Just because you and your drinking buddies think something is important isnt going to cut it.
After you, as the defendant in the original law suit, prove all that, then the other side (plaintiff in the defamation suit) gets a chance at a save–if it proves that it would probably win, then, even after you proved the above, the case will not be dismissed. See, not so easy.
So, going back to anaggrieved artist who tweets about the evil bastard Joe Doe who stole my illustration and then, worse, follows up with No one should shop at his store because he is a lying thief! well, that artist may be facing a lawsuit for those tweets and one s/he may not win. Think about that second part of the Anti-SLAPP–the potential save for the plaintiff–maybe Joe Doe had an implied license or a legitimate fair use defense that you, as a non-lawyer, didnt know would gut your infringement claim.
Better to sit on your tweeting/social media hands than run the risk of getting sued. Even if you did win, youd have to go through the unpleasantness of litigation. Instead, register your copyrights regularly and, if something gets used without your permission, talk to an attorney about your infringement claim and what your options are.
 And by say I mean speech made in any medium–wrote, recorded, painted, shouted in a public space, etc.
 Some other states have similar laws.