Everyone, no matter what position on the team, has to have ownership (or at least feel like they do!) of SOMETHING. People hate feeling like they are not being useful, or that their ideas are being ignored, or that they have no chance to affect the outcome.
Everyone can make a valuable contribution in some way. Sometimes you just have to figure out a person’s unique way of contributing. The answer that you get when everyone has contributed will always, no questions, be better than the answer had you come up with it alone.
No one thinks like me, as much as I hate it. Patience is soooo important. Honesty and immediate direct feedback is always the best, even if it is painful. You have to lay the groundrules for how this guy behaves on the team and interacts with others; if he’s being immature or can’t take criticism or whatever, let him know that his approach is unacceptable and why. Then let him know that if it continues his eval will say so. Then, if he still doesn’t change, blow it off. There’s nothing that you can do so don’t stress about it.
Humor, levity, and a certain lack of seriousness can be helpful in relating to others. At the end of the day, people at work are just that: people at work.