You don’t say!
Definition 1 of 1
Pro Tip 1/3Sarcasm Indicator
Shows disbelief or that something obvious was stated, often in a mocking tone. 
A: 'Gamers like video games.' B: 'You don't say!'
Pro Tip 2/3Not Literally
Don't take it at face value; it's usually not a request for more information. 
A: 'I finally cleaned my room.' B: 'You don't say!'
Pro Tip 3/3Casual Use
Commonly used in casual, informal situations among friends or peers. 
A: 'I ate way too much pizza.' B: 'You don't say!'