I'm currently on my first playthrough of Pokémon Violet and nicknaming every Pokémon I catch. I just caught a Summer Form Deerling and tried to name it "Summer Deer", but the game objected and said it wasn't allowed. (I tried "Sun Deer" instead and it accepted it.)
I can't think for the life of me why "Summer Deer" would be objectionable. Presumably there's some form of foreign-language Scunthorpe problem at play here, but what exactly is the game objecting to?