"Is it libelous?"

1. “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, this is not libelous. The reporter is merely incorporating someone's opinion into the article.
Some corroborating evidence would have to be used, but because the man is dead and was probably a public figure makes it difficult for his estate to sue the writer for libel.

2. “Megan Fox is a man!” Headline on Weekly World News Web site
Though the headline is a slightly malicious attack, the Weekly World News Wed site is a tabloid and most people do not take these stories seriously.

3. “In my opinion, Kevin is a murdering rapist.”
This could be proven libelous in a court of law. Prefacing the remark with "in my opinion" does not shield the reporter from libel claims.