short for "Oh Really Now!" which is used for several reasons to include: (1) As a response to when a person feels someone has stated something in a boastful manner, implying a high or superior status; (2) As a response to when someone feels competitive with another, or feels doubtful of another; (3) As a mood-elating fun statement.
(1) Frank: "I can bench press over 300 pounds."
Dan: "Oh Really Now?"
(1) Matt: "I cleared over 200k last year."
John: "Oh Really Now."
(2) Bob: "I used to run a mile in less than 5 minutes. I could do it right now if I wanted."
Bill: "Oh Really Now."
(3) "Oh Really Now! Orn!"