I've been very lucky to work with some very talented developers over the last 11 years. (Wow, I suddenly feel old :)
However, we've all been on those teams where there's been a primadonna, that one person who thinks he or she is God's gift to software, and that everything they touch turns to gold. These people typically see testers as evil little gremlins who are hellbent on destroying their perfect code. As such, they display a certain level of standoff-ness to testers; maybe they aren't willing to answer questions, maybe they dismiss bugs as extreme edge cases, you get the idea.
I've always believed that my ego isn't part of my work. If someone finds a hole in a test I wrote, it's not personal. They aren't criticizing me. Most people I've worked with share this belief. It's not fun when someone finds bugs in the code you wrote, but it's not a personal attack either.
Sometimes just having an open conversation stating the above to the primadonna corrects the problem. Other times, they get even more huffy. So here's a trick I used on one primadonna. He was starting to brush off some of the concerns I was raising. I lifted a finger and said to him, "Mike*, my job as a tester is to make you look good. And if these items get addressed, the product's going to work better, people are going to love it, and as such, you're going to look great. So come on, help me make you look great."
He gave me all the help I needed after that. Sometimes it's all in how you play things.
*Mike wasn't actually his name. I always change names to protect the innocent. Then again, I'm not sure how innocent he was. His name was Lou.*