I didn't know fruitcake was slang for someone who's a little off in the head.
ーFruitcake is slang for someone who is weird.
「Fruitcake はスラングで変人という意味がある」
〇〇 is slang for xx と言うことができます。
someone who is weird で「変な人」
ーI didn't know fruitcake was slang for someone who's a little off in the head.
「fruitcake はスラングで変人という意味があることを知らなかった」
someone who's a little off in the head で「ちょっと頭がおかしい人」
ご参考まで!