What does "you're killing us here" mean? Is it a general expression?
This phrase is a term of exclamation that can mean a few different things depending on the context of the conversation prior to the phrase being used. In this case, Joey and Ross are frustrated because they're waiting a really long time and they want to leave but they can't until Rachel serves the dessert. It can also be used used in a humourous situation. If someone is telling a very good joke you can say "you're killing me" to show that you're really enjoying the joke.