Okay, that gym instructror was completely childish and rude 🙄 if an adult thinks it's okay to laugh at something like that then there is something wrong with them emotionally 🤷‍♀️ I avoid people like him like plague. Those kind of people are toxic as hell and do not even care or understand how they are acting towards other people. I always say my last name first. In my country it isn't considered as formal as it might be in some other countries.