I don't really see "psychopath" in this scene either, to be honest. I see that version of Pinkie as just fanon, and it can be fun in fanon, but it's not what's going on in the show. The way I see "Pinkamena", and also the reason I continue calling this version of Pinkie by her full name, is that it's a coping mechanism; when Pinkie is faced with a situation when she has failed to make her friends happy, or is unable to make them happy, she reverts back to her foalhood state before she saw the rainboom and got her cutie mark. Her hair deflates and her colour fades slightly, just like she was back then, before she discovered her talent for making ponies happy