It is the combination of "Shut the f*ck up" and "Get the f*ck outta here." It is used to express extreme surprise or disbelief.
Dave: I've been having sex with my 40yr old boss for months now, and she just told me she's pregnant

Smitha: Shut the f*ck outta here, are you serious?!
by darbizwell June 16, 2010
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