[smacktoward]

This one's pretty easy: just be up front about it.

"I had an idea. I went out on my own to try it out. It didn't work out, but I learned a lot along the way."

Then just be prepared to talk a little about the things you learned, and how they helped you grow as a professional.

No employer worth working for is going to ding you for taking a risk like that -- even outside SV! Seriously! -- as long as you can make it clear that you really were working on something during that period, rather than sitting on the couch eating Cheetos.