How do I respond to "how do you like your program" if I completely hate it?

"My experience hasn't been great" is a clean way to indicate the problem without criticizing anyone. You may want to couple this with something honestly positive -- such as "I really like my research topic, but overall, my experience in the program hasn't been great."

If they follow up -- and they probably will -- you can say something like: "I've had a number of issues with the faculty. I probably shouldn't go into all the details though." In this way, you give a reasonable answer to their question without inviting further discussion. You can then redirect the conversation to something you're more positive about -- for example, your research or graduation plans.

Just flat up say something like “There are some things that I like, and there’s some things that I dislike, and that’s as much as I’m going to say about it because saying negative things about your employer is unprofessional.” That way, you can indicate your feelings about your situation both without lying and without acting unprofessional and saying negative things about your employer.

If they miss the hint, and continue asking questions, simply say, “I’ve already said everything that I’m going to say on the subject” or simply “No comment”. Eventually, they should realise that you were being serious about not wanting to talk about it.