Truthfully? It's a lot of forced bullshit based on stereotypes, in my opinion.

[He perked up with that. Absent-mindedly reached up to scratch at the back of his neck as he thought it over, the familiar touch of the scales gathered along random parts of his skin kicked him back to realization.]

Supposedly there's just this general misconception that oni and anyone associated with them are a bunch of hard-headed dumbasses. Doesn't it just piss you off? Make you want to show them up?