A mixture of "are you fucking with me?" and "are you serious?" commonly used when cut off by some dumbass driver, who was too stupid to get over when they were supposed to.
Also when you hear something completely unbelievable.
A stupid Honda cuts you off, almost causing you to text-end
so you scream "are you fucking me seriously?"
"honey, I think were have sextuplets"
"are you fucking me seriously?"