Koro-sensei's name is a pun on the words "korosenai" {"unkillable") and "sensei" ("teacher").
In Season 2 episode 10 "School Festival Time" at 18:01 very briefly, when people are standing in line, the main character of the the manga series; "The Disastrous Life of Saiki K." Kusuo Saiki can be seen waiting.
Throughout the anime, main protagonist Nagisa Shiota often finds himself teased by the other characters for his androgynous appearance; coincidentally, three of his four voice actors are women. French is the only dub in which Nagisa is voiced by an actor of his actual gender, with women voicing him in both Japanese and English versions.
In season 2 episode 4, all E-Class people are listed off by their "Code Names" in the cast section of the end credits.
In Season 2 Episode 10, a reference is made to the anime "Food Wars!".