I respond to, "I don't care," with, "well, since you're so uninterested, we won't worry about it. Moving on..." and just don't give them any of what they were asked to choose from. They usually quite quickly say which they prefer after that.
I was taught at school that refusing to make a decision makes things harder for your host, and throws their attempted kindness back in their face. If you really don't mind and all things being equal, it's best to just choose something anyway. I've always liked this advice.
My favourite PA people are those who moan, "oh, I'm getting so overweight, look how fat I am..." to which I also always agree enthusiastically. "Oh yes, why, I never noticed it until you pointed it out. Good gosh, look at your chins! I was sure there were only two last week!", with varying degrees of sincerity. Works well for grey hair and wrinkles, too. If I'm going to compliment you, I'll compliment you. Don't demand I do it (thus invalidating any compliment as not genuine anyway), and don't be all "woe is me" about it, or I'm just going to agree.