The same thing happened to a friend of my dad. A long time ago, the friend was a British diplomat living somewhere like Singapore and he made friends with the two Japanese sisters in the next apartment. They used to have tea and chat and he helped them practice their English. Being good with languages he soon picked up a lot of Japanese from them. One day he got invited to an event at the Japanese Embassy and was excited to be able to show off his secret language skills. However, any Japanese man he spoke to would react strangely and it looked like they were trying hard not to laugh. He eventually got someone to explain that he was using “women’s words”, and the effect of a dignified English gentleman in a tuxedo talking like that was hilarious to them.