"You ain't ready for this" is basically a way of saying that this is so good you might not be able to handle it.
"I could tell you what happened last night but I bet you ain't ready for this"
"You gotta hear these tunes, you ain't ready for these tunes"
"You gotta hear these tunes, you ain't ready for these tunes"
by TheeHitch December 10, 2013