Work problem I've never had (angst inside) →[More:]So this new guy has joined our department. He's super-smart and knowledgeable, and someone I thought/think I could really learn from.

He's been in our department for about six months, and, until now, he's been pleasant and enlightening to interact with. All of a sudden, we're assigned to the same project, with him as the lead, and he's turning into a total dick. I make progress on our project, and he's the first to jump in with something like "I don't think that's the right direction" without even backing-up his opinion. I ask for help or insight, and he gives me vague responses that don't really answer my questions.

Ok, so I get he's trying to assert his dominance and may feel threatened by my seniority (I've been there nearly three years, he's only been there about six months), and I'm more than willing to let him take the intellectual lead (I don't even want that responsibility, and I have very little interest in "leading" in general), but why on earth does he seem to be trying to make me feel/look like an idiot? Or is it just my own insecurity that's making this feeling way worse than it would be otherwise?

Has anyone else gone through something like this? I *almost* sent him a "WTF is going on?" email tonight, but figured it would be better to wait until I see how I feel in the morning. It just seems like it's quickly reaching the point where we won't be able to work comfortably together unless we somehow put our respective cards on the table.