I'm going to tell my coworker the truth about what we all think of him
Why do you want to do that?
Because he's a bad coworker and a dishonest person
That may be so, but telling a coworker that might not be professional. You don't have to like your coworker. If you have a problem with his job performance, you should talk to your supervisor about it.
You know, my boss always wants to hear about people's honest opinions, some people don't like that but I respect it and I'm always open minded.
Telling your boss is different than confronting your coworker. It might lead him to feel like he is being bullied or harassed at work which could cause trouble for you. You should report it to your supervisor.