I grew up in Lexington. UK fans never gave Louisville a second thought until Denny Crum became the head coach over there. He was always saying his players were better than Kentucky's. No one took notice until he started getting the really good Kentucky players, mostly from Louisville.
When Joe Hall was forced to play them, the hate was the result. Up until then, it was a rivalry only when we played them. In those days, Kentucky also choked against WKU, choked in the dream game and a few times afterward.
It wasn't a 24/7 hatred, though, until Pitino took that job and actually thought many UK fans would become UL fans.