what is the meaning of
Out of the blue? I just heard a conversation like below;
Jesus. Out of the blue, man. What brought that up?
what are the other possible cases that this phrase might be used?
It means "coming on you without warning" as if falling from the sky directly onto your head. "The blue" in this case is the blue of the sky.
This is probably derived from the old idiom "a bolt from the blue":
I have heard this did not originally refer to lightning, but to crossbow bolts in medieval times raining down after having been shot vertically. I'm not close to my reference materials at the moment, however, so I will look later.