I'm not sure who Red John is, it could be anybody really, but some things really irk me about certain characters.

Gale Bertram: In one episode where he talks about his poker game with Lisbon he says "gutted" him.
Also, in the same episode, but in an earlier scene where he was mad because he kept losing and Lisbon said that it was just a game he said: "You don't believe that" as if he was reading her.

Brett Partridge: This guy irks everybody, but what REALLY irks me is the fact that in the pilot, he said that Red John painted his face with a rubber kitchen glove. How could he know?

Walter Mashburn: He's in a "relationship" with Teresa, and Teresa is Jane's so I'm guessing that it'll be like O'Laughlin.

Kristina Frye: She knows too much and she didn't get killed, but abducted instead? I think she's one of the people Red John uses to keep an eye on Patrick.

Bob Kirkland: Now this guy is just an obvious Red John associate. He probably broke into Jane's place to confirm if Red John's list and Jane's were the same. If they weren't, he would've told Red John about it and consequently, Red John might have not given the video to Jane.

Ellis Mars: He is Mar

Rosalind Harker: She should've known that "Roy Tagliaferro" brought in a dead body, but she acted as if she didn't? That's totally not suspicious at all.

Bret Stiles: How did he know where Kristina was?