When sato kun died baka?
In ep 7, at around 7:46, you can see a silhouette of Bonta-Kun from 'Full Metal Panic: FUMOFFU' standing next to Himeji.
Episode 7. When Hideyoshi uses the Satelite Phone, the screen where he contacts "Pervert" is the same as the Codec screens on Metal gear solid 4. Even the same buton commands are present, with the same frames.
Ep 8 around 3:38, the symbol in Muttsuriini's eyes are those of Geass from Code Geass.
Ep 8, around 4.16 you can see a flipped symbol of the NERV logo from Evangelion, except it says BAKA instead of NERV
Ep 8, around 7:23, Muttsuriini's summon is dressed in the same style as characters from Peacemaker Kurogane.
Ep 8 around 7:33, the scene involving Yuuji and Muttsuriini's summons is in a style similar to those used in BL's.
In ep 10, the art style used around 21:34 is in the same style as the painting "The Scream" by Edvard Munch
In ep 11 at the start of the ep while they play rock paper sissors and later on in the ep during their battle there are references to sayonara zetsubou sensei. In that anime they often have constantly changeing random facts or references on their blackboard.
Episode 11. At the start of the battle when Yoshii is sent to scout the battle field, he infiltrates the enemy lines covered with a cardboard box, and the D class members call him "Snake?". Reference to Metal gear solid saga Solid Snake who has always been provided with a cardboard box as his basic and not so effective infiltration tool.
Episode 11. When Yoshii returns from challenging B Class he's dressed like, and has the stars on his belly that parody those from "Fist from the north star"
Episode 11. One of the B-Class members is a Hatsune Miku parody from Vocaloid. You can see her a few times, one of those from her back when Yoshii starts hiting the wall for the surprise intervention.
In ep 1, at 10:42 one of the student's said "zetsubou shita" which is the famous line of itoshiki nozomu-sensei from sayonara, zetsubou sensei
Kinoshita Hideyoshi most probably got his name from HIDEYOSHI Toyotomi with his old name Toukichirou KINOSHITA, who was a daimyo in the Sengoku period.
In Chapter 9, you can see Himeji in an attitude similar to that of the first arc of "Higurashi No Naku Koro Ni", which are transformed in the eyes of Rena and Mion
In one of the movie posters in episode 3 (the one that looks like Apocalypse Now), the names of the characters are listed as the "cast" of that movie. The romanization of the names would use a "Z" instead of a "J" though.
In episode 3 at around 6:53, many game titles make an appearance as parodies: Love Minus (Love Plus), DoraDora Quest (Dragon Quest), among many others. Game consoles and Game Manufacturers are also parodied
In episode 4 at around 9:52, Aki mentions something about "I almost got taken through the gate". The preceding scene to this line is most likely a reference to the shadowy hands of Hagane no Renkinjutsushi (Fullmetal Alchemist)
In episode 5 at around 9:46, Tsuchiya Kouta performs three consecutive "SEED modes", reference to the Gundam SEED series
In Episode 05 at about 10:38 Akihisa performs the "Problem Breaker," a clear reference to Gurren Lagann's "Giga Drill Breaker," by throwing his Striker Sigma V into the ground while it spins like a drill.
In Episode 6, Yuuji holding a plastic with a logo reminds of the store named 7-Eleven, and Yuuji is holding a Coke reminds of the brand named "Coca-Cola"
In episode 6 around 17:00, Kouta Tsuchiya sinks into the pool after having a nosebleed. As he sinks, he lifts his hand in the same fashion as the final scene from Terminator 2: Judgement Day.
In Episode 7, Yuuji and Shouko imitate the Front Boat Flying scene of "Titanic", and Kouta is dreaming about "Titanic" stars like Leonardo DiCaprio and Kate Winslet
In episode 7, at 12:18, the first movie that's being displayed by Hideyoshi is the 1994 release Speed.
In Episode 8, Himeji's summon cosplay of Morrigan of Darkstalkers, Minami's summon coplay of Lilith of Vampire Savior, Hideyoshi's summon cosplay of Baby Bonnie Hood of Vampire Savior, 3 of the Capcom Characters
In Episode 8, Yoshii's summon and Himeji's summon reminds the fight scene of Force Impulse Gundam versus Freedom Gundam of Gundam SEED Destiny episode 34
In episode 8 around 12.47 you can see Souichi sneaking towards Yoshii while inside a card box. This is a reference of Metal Gear Solid game series' trademark move by Solid Snake, who happens to share the same seiyuu as Souichi.
In episode 8, the scene at around 12:13 where Yoshii is in agony as a result of the attacks by the summoned creatures of Yuji and Mutsurini and all the imagery that follows until his creature's death is a parody of Evangelion.
In episode 8, the pose that the school principal makes at around 19:01 is a parody of Ikari Gendo's famous pose in Evangelion.
In episode 8, while walking in the vents for the second time, Yoshii's summon appears in what is the underground level of Nintendo's Super Mario Bros. A mushroom also appears that causes Yoshii's sumon to grow in size.