Different dialects

Chinese people have different dialects depending on what part of china you came from. I speak a different dialect at home. It's not Cantonese or mandarin. I could speak Cantonese cause I learn how to speak it from friends and watching Chinese drama. I understand mandarin but I can't speak it. Today in front of my building my co workers from another department was talking about me. I know who they are and they know who I am but I don't speak to them. They were speaking in Cantonese saying I was skinny when I start working here. Then I blew up like a ballon. Now I'm skinny again. They were gossiping saying maybe I throw up my food that's how I lost the weight. They didn't know I understand Cantonese. They were standing really close by. I let them finish there conversation. I call them a say baht por it means bitch in Cantonese. They were kind of shock. Never judge a person. You really don't know these days who understands other languages. I work with naive people.