It happened in Paper Mario: The Thousand Year Door. One of the side quests you can get from the quest board sends you to a toad (I think) who says Luigi is their favorite. If you put on a badge that gives you Luigi's colors and talk to them again, they freak out and get so excited. Then Luigi walks by and is like, "hey, what's up bro? Why are you dressed like me?" The toad gets upset and starts shaming the real Luigi for going around pretending to be Luigi haha.