Master of Hentai. Tends to spend all free timewatchinganime porn. But you can't be just any watcher of hentai. To become master you must wank uncontrollably for an entire day. Then and only then will you be Hentai Senpai.
Boy 1: Hey look at that nerd over there! I bet you he has no friends!
Boy 2: Are you kidding? That's Hentai Senpai. He may not have friends but so many guys look up to him! I can't wait til I can one day become like him!
Boy 1: He's still a nerd.
A Japanese honorific used when someone is older than you in age or they have more experience in a field than you. The opposite being Kouhai
It is usually a troup in anime or manga for a Kouhai to desperately seek their Senpai's attention but fails as because their senpai ignores them continuously.
"Kumagi-senpai was really nice to me today. He even offered me to go drinkingwith him after work!"