Bring your half-baked idea to the Half-Bakery
halfbakery.com
halfbakery.com
If someone guardedly shares their own half-baked idea over dinner (especially if they think they need to find a technical partner, investor, or get a patent), rather than give them a lecture about customer development, I tell them it sounds interesting and send them a link to Half-Bakery or http://www.cambrianhouse.com/idea/.
The hit rate is shockingly high. And even if they don't find their idea, they'll realize ideas are a dime a dozen and start focusing on how to validate whether their idea actually has legs.
edit: there->their
I had several (ridiculous) ideas while I was an undergrad and I remember how pleased I was when I found other folks had posted similar ideas on Half-Bakery. In fact one idea actually did end up on supermarket shelves (albeit in a different form).
Sure, i get annoyed every time the 500-mile email or more magic or some other classic story gets reposted, but that's what HN is about-- every time it's reposted, there are dozens of people that hadn't seen it before.