When Amy tells her that Sheldon was hurt by it and that she thinks Howard should apologize, Bernadette isn’t sold.
So, she goes to Bernadette and asks if she saw Howard’s costume, to which Bernadette replies that she made it.
Bernadette believes Sheldon shouldn’t dish it out if he can’t take it, and she and Amy end the conversation at a tension-filled impasse.
She brings up the fact that Sheldon always makes fun of Howard being an engineer and where he went to school, and has even called baby Halley Winston Churchill, all without apologizing.