I would actually feel the same way. To me, this type of reaction would sound dismissive and borderline condescending. When I want to address something seriously, especially in therapy, I expect to be taken seriously. When I had therapy I definitely didn't come to sessions and paid hefty fees to entertain the Ts. There are certainly moments when both client and T can naturally lighten up and laugh at something together, but it has to feel funny to both. If it is habitually funny to the T only, this is inappropriate and unprofessional. I would definitely tell them that I don't appreciate their having fun at my expense (literally) when I am trying to discuss some serious stuff about myself and my life and that I want them to focus on what I am trying to say instead of finding fun in how I say it. I had only one such moment with my last T and I told him exactly how I said it now. He did shut up and never did it again and was really trying to listen ever since.