Puberty

S1, E6: The Timmerman brothers, the one hit wonder brother band from a few years earlier, visit the music video set and terrorize Nat with the horrors of puberty.  Nat becomes convinced his voice is changing (turns out it was just a cold) and Alex does everything he can to convince Jesse he's old enough to "really" date her, including drawing on underarm hair and pretending to read thick volumes of obscure books.