So, let them. And now you know.....
This opening idea is not the only one that you will ever have. And since this is really a test balloon to verify that you understand the company, its structures and way of doing things. Having this co-worker run with your idea will show you who you should have brought it to in the first place.
We can't always be protected and honored for our ideas. Some of the most successful men in history routinely let other people take credit for their ideas. I am not advocating this in all industries, but getting the credit is not always the best thing.
For instance, this beer buddy takes your idea and runs with it, and then getts shot down. Now you have information on the idea thief, and those involved in his ambush.
Really this is probably a no-lose situation. Your first idea may not be your best idea anyway. You may very well come up with a better idea or a way to improve it after it is stolen anyway.
