Originally something he heard from his dad, this is a folk simile my informant sometimes uses. He told me his dad spent a lot of time in Australia, which is where he picked it up. It’s used to talk about someone who is angry or annoyed, comparing them to a snake that has been cut. I’d never heard the simile before, but it makes sense, since people always say to be careful around snakes and that disturbing them all could make them angry enough to attack you. Cutting them would provoke an even larger response then. It’s also clear why this came from Australia rather than America, for example; Australia is a place where dangerous snakes are more common.
My informant said he liked the saying because it’s different; he hasn’t heard other people use it really. It also reminds him of his father, a man he loves and respects. I heard him use it once when describing a bar fight which erupted after one man slapped another in the face. The man who had been slapped was embarrassed, since he took it as a shameful thing to be slapped, and he became very angry. My informant said he got as “mad as a cut snake.”