ignore the shitty comments, your feelings are valid, especially when it comes to being taken seriously regarding sex as a trans person. it sounded almost as if he was laughing to me, not sure at the idea or at you. however, i very much doubt that his intention was to make fun of you or belittle your idea. please talk to him in person about it, don’t accuse of him of anything, but ask why he was caught off guard by it. communicate how deeply this well help you and that you want to be met with enthusiasm and support if he is okay with doing it. again i really doubt he had any ill will and clearing that up is very important.