[Frqy3]

Early in my career someone taught me a useful technique for dealing with this situation.

After each "new" idea, spend about half an hour working on the idea. Best to do this on paper and target producing some good looking notes. Then file it away close at hand. If the "idea guy" ever follows up and asks you about their idea, pull out your notes and say "ahh yes, I've been working on that and I have a few things to discuss with you." You now appear as a hard working and enthusiastic underling. For the majority of cases where they never follow up, you have limited your wasted effort.

[DanBC]

Wouldn't this risk the idea guy latching onto you as being the first person who has shown interest (or, in the idea guy's mind, the first person who sees the real potential of my genius)?