Person 2: No shit
Dude 2 - "No shit."
*Dude 1 tries to think of a comeback*
Dude 1 - "...So, how 'bout them Red Sox?"
First case: often said slowly, emphasizing each word and with "shit" often raised slightly. = "You don't say"
Second case: usually said quickly and without as much emphasis, for you really just want to get on with your life and not listen to this fucktard anymore