Meaning/Usage: Common way to express disbelief
Explanation: You are not telling someone to literally get out. This is a common idiomatic phrase to express disbelief. Often times it is used in a positive way as in the first example sentence below.
"Get out of here! We actually finished in first place?"
"Get out of here. She would never say such a thing about me."
"Get out of here. That's hard to believe."
A. "Jen told me that Ryan got an A on his test."
B. "Get out of here! He didn't even study!"
A. "I'm telling you the truth, he got an A."
B. "What a surprise."
Other Common Sentences
"Are you joking with me?"
"Are you serious?"