I don't feel like he has cracked. I only have limited experience with Grammaton, but my impression is his tolerance for what he finds to be stupidity is currently running at a low, and as a result he snapped rather than handling it with composure. I can't really go into too much detail because it pertains to a game running elsewhere that is currently ongoing, but I don't think a Scum!Grammaton is so nervous and on-edge as to be wary of simply this much "pressure". Throughout the exchange, I agree more with him than with you, obviously taking aside the slur.