I hate to give the stinkweed credit for being a threat but I think that's exactly what he was to at least a few players.
Tom had to be really nervous that Steph might have told Coby of his F4 plans with her. He doesn't know if he can trust her or not at this point. If she told Coby and Coby tells Gregg and Jenn that Tom has no intention of taking them beyond F6 and F5, he can easily turn the tables on him and get them on his side to boot Tom and Ian first ( ala John/Zoe alliance- Marquesas).
Gregg had to be worried also that Coby would share his secret that he and Jenn are ready and willing to turn on Tom alliance. If Tom found out, Gregg and Jen would be the next to go.
Steph was thrown a lifeline with Coby as the target and she took it. Her only motive was at least it wasn't her on the block.
Katie didn't like Coby at all, I don't think she was worried he would say anything, she just thought he was a PIA.
Caryn surprised me with her vote. I was under the impression they were friends and had an outsiders alliance but she probably got sick of his whining.
Jenn thought he was a combination of threat and annoyance.
Knowledge is power and Coby knew some secrets or was perceived to know. Coupled with shooting his mouth off openly AND being whiny and annoying, that would make anyone nervous enough to get rid of him before he gets rid of you. He was a threat, certainly not as much of one as he seemed to think he was though.