Im sick of my dad and his girlfriend

Every single time I say anything at all they make an joke about aliens have taken the past me. Or the space ship is waiting outside for me. At first I laughed with them , But then it was constant and every time I said one thing , then it got annoying as I couldnt even say I felt depressed without them making the joke. Im very thick skinned as I have to be for my line of work and I love jokes as I make them about myself too but when its the same joke constantlly no matter what I say thats when I get pissed off espically when they do it when I try to have an adult conversation. They have been doing it since I was 16 so just now I told them im getting bored of it and now they are mad at me. I dont know why It taken so long , but Maybe I did say something as an teenager , I most likely did but they still continued. I know I have an lot of past trauma , and they are maybe trying to make light of me being too mature for my age and forward which I appericate but I just dont appericate it being constant as its mocking everything I say.