As Scarce already noted, it looks like Jack Conway's recent ad going after Rand Paul really got under his skin. They went back and forth over the ad several times during the debate and at the end, Rand Paul refused to shake hands with Jack Conway and walked off the stage in a snit.
Update: TPM has a great post up summarizing some of the back and forth during the debate which you can read here -- Rand Paul To Jack Conway: 'You Demean Kentucky'. And here's the video to go along with their post.
I'll just add that other than Paul looking completely rattled by Conway's recent ad, I think Conway did a really good job over all during the debate. He hit Rand Paul time after time for his extremist views that he's been trying to walk back during the campaign. You can watch the entire debate at C-SPAN's web site here.