Inoue Kenji, author of Baka to Test to Shoukanjuu seems to like giving the characters old-fashioned anime nicknames or from strange sources.
Such is the case of "Tetsujin" Fujiwara-sensei, who either is named after old mecha anime "Tetsujin" or from a yearly extreme sport even known as the "Iron Man Triathlon" (which I don't know if it's still being hold).
But the one I would like to know the source is Tsuchiya "Mutsuriini" Kohta. At the starting of the 3rd novel it was stated that it came from him being extremely perverted but he adamantly denied it. Does it come from an old anime (and which) or is it a japanese slang term? Thanks in advance.

According to the wiki, his nickname derived from his sullen personality (muttsuri) and suffix -ni to even it up, hence muttsurini. As of why it's a parody for the Italian fascist Benito Mussolini, my guess 'cuz they share the same 'unusual' large eyelids.

Thanks.