Things follow as you would imagine. The four guys bond by hanging out in the parking lot of the local Pizza King, stripping their friend down naked while he's wasted and egging the house of the still-hated principal. No wonder their wives are annoyed. The film is pretty gross, featuring vomit, fecal matter, and multiple farts in almost every scene. The assistant principal turns out to be the gay lover of the principal, and you know how we know he's gay? Because he shows up at the door of the egged house, and he's actually holding a little yappy dog.
Haven't we moved past the days of "St. Elmo's Fire", when the one gay character is shown swishing through the hallway holding a girlie drink with a colored umbrella in it? Even more disturbing, in "Back in the Day", the fact that the principal turns out to be a gay man is supposed to make us see him as ludicrous and worthy of mockery. The four guys are always joking about having anal sex or raping each other. They live in terror of penetration. I get that this is sometimes how guys talk, but it's not treated honestly here. It's an unexamined cliché of male bonding. It's lazy.