Could you introduce some other example questions of "Since when ~"?
Native speaker’s answer
Rebecca
The expression "since when ~" is used to express surprise, frustration, or even anger towards something that someone has said or done. Although "since when ~" is asked as a question, it is used more as a hypothetical question to indicate one's surprise without actually expecting a response to the question. Ex: Since when did you start borrowing my clothes? Ex: Since when is it okay to lie?