I guess this page wasn't enough for people to see that the knife was a visual metaphor. Mayu is not actually threatening to murder her girlfriend; the danger here is making her sad, which is being exaggerated for comedic effect.
She tracked down the baker. That is insane.
And even with the knife being just in the girl's head, that her mental state defaults to that imagery points to a huge issue with the relationship. A crippling fear of disappointing your girlfriend based on it happening it before isn't good.
Like, I get this is supposed to be played up for comedy, but I just don't find it funny. It's the same as me not finding abuse played up as slapstick funny.