Is it libelous?

1. “Megan Fox is a man!” Headline on Weekly World News Web site
NO: it doesn't ruin her reputation because no one would believe a tabloid that specializes in hyperbole.

2. “Up until the day he died, he was a brilliant writer. But the drugs made him a thief, a pimp and a liar,” said friend Karen Smith, who was with Johnson at the time of his death.
NO: when someone dies, they cannot sue for libel

3. “In my opinion, Kevin is a murdering rapist,” the prosecutor told the jury.
NO: journalists are protected when reporting on court cases

4. "In my opinion, he's a murdering rapist," the man said at the rally.
MAYBE: it depends on the context; who the man is, where he was at, etc.