The phrase "you don't say" can be used to express surprise, disbelief, or sarcasm in response to something someone else has said. There are many synonyms you can use to convey the same sentiment, including "no way," "seriously," "are you kidding me," "get out of here," "for real," "tell me more," and "you're joking." These phrases all suggest some level of disbelief or incredulity, and can be used both sincerely and ironically depending on the circumstances. Whether you're genuinely surprised or just being playful, there are plenty of ways to express yourself beyond just saying "you don't say".
