A haircut fetish is when one is turned on by cutting, dyeing, and/or shaving someone's hair.
Guy 1: Whoo boy, Sofia is hot!
Guy 2: Why? To me, she's only a 7.
Guy 1: She is the definitive pick of a haircut fetishist like me. I want to cut her hair, dye her hair like Kylie Jenner, and then shave it all off!
The Hentai Protagonist Haircut (or hph for short) is that generic haircut dudes get looking like a damn bowl on their head. Literally the most boring possible haircut a dude could get.
Person 1: Hey did you see Dane's recent haircut?
Person 2: No, what does it look like?
Person 1: He's sporting a damn Hentai Protagonist Haircut