I still see JDs very low on the aggro scale. I don't consider them as bruisers on average. I know that there are a few out there that are real aggressive, but not enough to gain a reputation. I think your friend probably has never had any other large cichlid other than his JD. If he had a Red Devil, Jag, Uro, or even a Salvini, he probably wouldn't be bragging so much about a JD. But like someone mentioned earlier, the only way to truly test the toughness of his JD is to pit it against another mean cichlid. And that would be cruel and juvenile. Fish have diverse personalities, no matter their species. I've seen some really big and mean fish get punked by some very small but brave fish.