My FIL has a lot of really bad habits, but only one is sufficient to drive me to the brink of insanity. The man cannot just say "thank you" for whatever you give him. Every "thank you" comes with a monologue about how he's sure it'll be okay, but he doesn't want to play with it just now, in case it's terrible, but it's kind of you to think of him, and he's sure it'll be fine, but he just has to think about what if it's not fine...and so on, ad infinitum. Every gift we give to him gets this reaction - even the things he's specifically asked for. We gave him a copy of "Killing Lincoln" by Bill O'Reilly last year - a book he had asked for by title and author. When he opened it, the response was "Gee, thanks. I'm not sure if I'll like it, but I'll definitely read it. I hope it's good. If it's not, I don't know what I'll do with it. But I'm sure it's good. I don't want to open it now, in case it's not good though, you know?". I said, "FIL, MIL said that you'd specifically asked for this book. Is it the wrong one?". He said, "No, no, I'm sure it's the right one, if that's what she said. I just don't know if it'll be any good. I mean, I'm sure it's good, because I said something about it, but if it's not good, I don't know..."
EvilMe would dearly love to ask for the present back when he pulls this, because obviously it's not what he wanted, and I wouldn't want to burden him with an unwanted gift, right?
Disregarding that solution, what is a good way to respond to this kind of "thanks"? It doesn't feel like a thank you at all, because he's so obviously dubious about what we've given him.