I would cull. A cockrel that is a jerk, is likely to remain a jerk. I would not pass him off to an other flock owner. It's theorized that nasty roos beget nasty roos. Don't know if that's true or not, but assuming that temperament is an inherited trait, I do everything in my power to see to it that a mean roo doesn't get to play in the gene pool. That means, he stays here and gets culled instead of going to an other flock to breed.