I know a few
Mario could have farted in Luigi's face, or Mario dressed himself as Daisy and the rest is yours to make up, Mario could have eaten all Luigi's cake from Peach (Got that idea from Super Mario 64 DS), Mario made him do with Wario,Luigi and Wario didn't notice and the both ran after him (Wario is slow, so he wasn't seen in movie), Mario killed Luigi's girlfriend Daisy :O , Mario spread out embarresing pictures of Luigi, Mario screwed up Luigi's party, Mario dressed himself as Luigi and made a fool out of him, Mario putted a crocodile in Luigi's toilet and that crocodile bit his ass, or a spider in his bathtub, that made him ran out the bathroom naked and everybody was watching, Mario secretly taped Luigi doing it with Daisy and sended it to the T.V.station so that everybody who watched T.V. saw that and the last one is that Mario just turned off Luigi's nigthlight. Great flash, can't wait. Hope I'm not too late for idea's.