Or you might end up with embarrassments like this.

Tina: Sir Santos is so dumb. I joked in class and he didn’t get it! HAHA!

Noy: Is Mr. Santos here in FB? Erase it Tina or he’ll see it. Your joke (in class) was funny there, hehe
Shiela: Dude Sir Santos is really dumb, hehe.
Professor Santos: Very funny, Tina. Well I have a very special surprise for you in class tomorrow. You’ll be getting a different exam. It’s more difficult than the normal exam. Give me a formal apology and I might reconsider. And as for you Shiela, we need to talk tomorrow.
Shiela: I’m sorry, Sir Santos

Just because there’s freedom of speech doesn’t mean you can evade accountability and walk around irresponsibly.