It at first seems baffling that Sousuke's teachers wouldn't suspect his guns were real, until you realize that Japan has very strict weapon control laws. Seeing even just a handgun in real life is unthinkable for a Japanese civilian, to say nothing of the military-grade assault rifles that Sousuke was packing.
Sousuke's inability to realize the fuss about the Sacred First Kiss might appear strange until one realize that he grew up in Afghanistan, where kissing (between men) is simply a form of greeting with no romantic implications whatsoever. In episode 8, he even revealed that he had kissed men before during his time in the Middle East and Central Asia.
Why is Kaname an extra harsh tsundere? And Tessa so openly flirty for her age? Their heads are always filled with whispers, so to get out what they think for themselves they say it out loud.
Related to that with Kaname, the whispereds get the thoughts of geniuses from the future and the past almost all the time, her having conservative opinions about how men should act probably comes from hearing the voices of old.