Also, they can only sue you for slander/libel if you KNOWLINGLY said false statements about another person. "Jennifer Lopez had liposuction" when you knew for a fact that she didn't.
However, relaying first-hand knowledge "he flies into a rage", if you know that to be true based on your own experience, is not libel/slander because it's a true statement. Now he if can show that you knowingly lied about that, which would be very difficult for him to do, then he would have libel/slander.
How do I know? My ex-father-in-law is a child molester. The last time he sent my girls gifts, i returned them unopened with a letter stating that he is to have no contact with my daughters because he is a child molester. He threatened me with a libel/slander lawsuit. I turned it over to my lawyer...who informed him and me that based on family information (his daughter's attempted suicide and his step-daughters acknowledgement that he had molested them), what I said was not knowingly false, therefore, no libel/slander occured.