When someone uses your idea.

[Audrey Quest]

"You might want to come up with something else because that's the exact idea that I shared with the class last week and its the one I am doing."

[onyonryngs]

Sharing ideas is a big part of the class so it wouldn't be possible to keep all ideas to myself. The question is more, how do you maintain intellectual property rights (so to speak) in these types of situations. I am glad to hear that it's not rude to be direct about it.

It's not rude to be direct, but I'd be very careful about how you approach it to make sure you're not coming across wrong because pointing out how much better you'd do on the project didn't come across well.

[Shoo]

"You might want to come up with something else because that's the exact idea that I shared with the class last week and its the one I am doing."

That's what I would have said.  I'd have definitely let her know I knew she got the idea from me.