One of my students is careless. Once he was studying Kanji, and a question required him, "Answer the pronunciation of 空." The correct answer is Sora(そら), but he wrote down Soso(そそ) in the answer column. It means vulva in some Japanese dialects, particularly in the vernacular of Kyoto. When I saw it, all I could do was to hold back my laughter. I was about to say, "Hey, don't write such a word. Do you know what Soso means?" but I shut up my talkativeness. He is still in elementary school, so he is too young to know the meaning of Soso.
Denshi-renji means microwave oven in Japanese, but I knew that quite a few people misremember denshi-renji as renshi-renji. One day I heard that it is hard for a part of foreigners to distinguish the Da-row from Ra-row in Japanese, but it might be only a matter of degree. It seems that a portion of the Japanese native speakers cannot make them out.