I'm having so much fun thinking about the interactions between Regina and Rodrick.
I think they would have a blast threatening Greg. Greg would say something like "She said she would cut me up like sushi and feed me to the zoo alligators" and Rodrick would be legitimately impressed. And Rodrick would catch Regina biting her mouth trying not to laugh when he threatens Greg in front of her, ask if she liked it, and she would deny it.
I imagine the shock in Regina's face when she meets his family for the first time. The classic "how did this come from that" situation. Frank being the definition of boring, Susan trying her hardest to impress Regina, Greg and Manny being the little shits that they are, and meanwhile Rodrick is the dumb punk mess that he is. His parents being so sure that Rodrick likes her, Susan trying to nudge them together at every chance, and Frank being completely at a loss about how his son even talks to a girl like this being who he is. Rodrick switching back and forth from vehemently denying to his parents that they are anything romantic (because he's dumb but not that dumb and Regina would certainly kill him at school if he implied otherwise) to looking at Regina with literal heart eyes trying to talk to her.
You know how Regina, at the end of Mean Girls, uses sports to channel her anger into something productive? Imagine if, because of Rodrick, she started channeling her anger into punk music instead. Just screaming into a mic for 3 minutes straight and Rodrick being mesmerized like "Wow... You have so much talent" and asking her to be a part of his band (none of his bandmates agreed to this).
Regina roasting him every chance that she gets—which is a lot, because Rodrick is always trying to get her attention. Rodrick is just glad she talks to him at all. Regina would be impressed by his resilience if he wasn't so annoying.
Karen and Rodrick agreeing with each other every time one of them says something dumb. Regina shooting daggers at Gretchen to make them stop, and when she fails, Regina just has to take matters into her own hands—otherwise she might get an aneurism hearing these two.
The Plastics putting up posters around the school for people to vote for Regina for Spring Fling Queen. Rodrick covering them up with his own posters for his band performing at some local venue (and maybe stealing one of the posters for himself if it has Regina's picture on it). Regina going at him because of it, trying to intimidate him into stopping. He doesn't stop—if it is because he wants to rile her up or because he was too dumb to be intimidated, is anyone's guess.
