Start with no thank you
Repeat no thank you
Change the subject
Repeat not thank you
If they push say you are not a fan (or it does not agree with you) of x - the more generic the better. (for me i do not like pie - I will not eat it - if offered a slice of apple, pumpkin – whatever, I am not going to say I don’t like that specific pie I am going to say I don’t like pie) the more generic you can be the less insulting you are.
No thank you should be sufficient, but I say if they want to push, be honest, and be unapologetic (about your dislike) you are entitled to dislike something, and if they want an answer give it to them. Don’t feel guilty, but also assure them it is not their fault, and you are not offended, and you are perfectly comfortable with your preferences and situations – assure them that they are still a wonderful host.