Anger flashes in Crowley's eyes. Even from a logical point of view, he's still more helpful than nothing and Dean's got information that they obviously wouldn't have had the last time that they apparently tried to work together.

He's angry, but he's also stuck on something. What comes out is a stilted, angry, "There's nothing half about me."

Regret? Crowley's biggest regret is that he didn't arrange for an accident for Dean right when he and Castiel first struck up their little deal. Dean's ruined everything since the moment he showed up with his boyband hair and his homoerotic relationships.