Chef begins to sing this to the boys, after they tell him that they think they killed Ms. Choksondik. Mistaking their Sea Men for semen, the boys explained to him that the police found the brine shrimp they put in her coffee in her stomach.
However, as he sings the song, Chef comes to the mistaken conclusion that the boys took turns raping and then killed their teacher, misconstruing "Sea Men" as "semen". He then stops singing and pushes the boys out his front door.
Sometimes you kill your teacher
and they find your semen in her stomach,