If you're nervy, you're so outspoken and brave that you're almost rude. A nervy student isn't afraid to ask even the grouchiest teacher to explain why he's giving so much homework on a Friday.
You can use nervy to simply mean "brave," but it usually carries the implication of being a bit of a smart aleck. Your nervy questions at a job interview might be seen as refreshingly straightforward, or simply cheeky and impudent. Sometimes nervy instead means "nervous," like a nervy tightrope walker who trembles and shakes with fear, but this meaning is more common in Britain than in the U.S.