Can you sue someone for gossiping about you?
In most cases, no. There are many things that have to be met for it to be considered that someone is breaking the law by talking about you.
For something to be slander, two things must be true:
1. The gossiper must show a reckless disregard for the truth. Just being wrong isn’t enough. You have to prove that they knew the truth and intentionally said something else.
2. You must sustain real and actual monetary damages. Hurting your feelings isn’t enough. Their actions actually have to directly cost your money.
If those two things don’t exist, you don’t have a case for slander.
Now, let’s take this out of the CIVIL realm and move into the CRIMINAL realm…
Yes, we all have the "Freedom of Speech" in the United States. However, there is a big exception to the Freedom of Speech called the "Fighting Words Doctrine".
If the words you are saying would make a reasonable person want to fight you, then you are not free to say those words. By saying them, you could be arrested for Disturbing the Peace or some other civil disobedience charge. This, of course, depends on the size of the audience. If the audience is small, you could perhaps see about charges of harassment.
Either way, you’d have to present evidence to the police (and subsequently to the District Attorney) to see if they’ll press charges or take other actions to curtail the activity taking place.