So.. when Stede teaches Ed on the matters of cutlery and dining, Ed reacts with physical violence to the slur he's been called. Stede tells him not to do that and respond in kind as not to let his opponent know he's hit the mark.
Later at the ship Stede gets subjected to ridicule and disregard and Ed chimes in. I read some very good meta about how this is Ed protecting and redirecting. He's basically doing what Stade thought him BUT it's still gotta hurt. Stede of course keeps his composure and laughs along but, as a victim of bullying myself, let me tell you it still hurt that Ed jumped right in instead of standing up for him in a more overt manner (just like he did with CJ by the way). No one ever took a stand for Stede, so he's not surprised that Ed doesn't. He's just a bit hurt and disappointed that not even a man that doesn't stick to the rules of society slips into that same path so easily. I wager that Stede doesn't fully understand that Ed is trying to redirect the attention away from him and for a good reason at that as well.
BUT then Ed gets hurt and mocked , and again does not instantly revert to violence but with a delay. What does Stede do? He steps up, spectacularly so. He goes right for the jugular with all the weapons of his class but then he doesn't stop there. When things go violent and dangerous, he delights in it. He utterly enjoys the chaos he singlehandedly caused on behalf of Ed. Ed, who is very confused and maybe a bit scared (Stede is so much more than the soft idiot he thought he was) by what he's witnessing.
The thing is, that Stede did not only avenge Ed. He got back at them for himself as well. These people in particular as well as their class in general - he is for once making a stand for himself. Destroying them as stand ins for every humiliation he has suffered at their kind. He merged his own and Ed's intrinsic reactions to ridicule and humiliation and obliterated those assholes completely.
He's doing for Ed, what he wished someone had done for him, what up until then, he couldn't do for himself, as he was suffocated by societal standards.
