I try to be gentle with my friends, but anyone who knows me a little would have picked up on the fact that the feedback I was offering (on request) wasn't positive. The sad thing is that this friend is a bit tone deaf. As an entrepreneur, that's probably a good thing at some level and a bad thing at another. It's a good thing because if he/she doesn't believe in the idea, he/she will be derailed and may not build a potentially great company. Moreover, there have been some great entrepreneurs who were never able to raise venture money for their endeavors. Tom Seibel is a great example.
It could be that I just "didn't get it." However, I was sad that my friend seemed so deliberately deaf to feedback. In the months that have passed since we last gotten together, not much had changed. Eric Ries, speaker extraordinaire on "The Lean Start-Up" www.startuplessonslearned.com is far more eloquent on this topic than I. He goes into terrific detail on how to think about developing a minimum value proposition (read: how to fail quickly). It is key for an entrepreneur to figure out if he/she has a great idea or if he/she is simply having a conversation with him/herself.
The thing that always surprises me about seeking feedback and not listening to it is this: the most valuable asset one possesses is one's time. The opportunity cost of not pursuing a different potentially great idea is huge. So, at the appropriate times in a new venture, measure success, come to terms with its success or failure and take appropriate action quickly. You will be happy you did.