It happens. One person has one opinion about a book or film and another person decides that opinion somehow threatens them. This seems to be more pronounced the more detailed and supported that opinion is by the text in question. Sadly, some seem to consider such thought out personal conclusions as personal insults (which they usually aren't) and react accordingly.
Unfortunately for them, most of the time their rebuttals are usually not as well thought out as they might be. Thus one can come up with a list of pre-thought out responses ahead of time beforehand and have some idea of how not to take such things personally and respond in such a way that even if the original party doesn't realize it, most other people will realize that they are being an idiot and that you did have a point (even if they don't share it).
1) “Don't like? Don't read!”
There are so many variations of this and it is used so frequently by everyone under the sun that it bears a mention. Fortunately this argument is exceptionally easy to apply the hammer of logic to. “How will I know I won't like it if I don't read it first?”
1a) ”Why do you keep reading if you hate the books so much?”
This is easily answered by noting that things change and there's always the possibility of future improvement. Frequently the person asking this question likes the status quo and would look unfavorably at change.
2)“You are not the target audience.”
This is a flawed argument as it implies that a reader or viewer has no active role in deciding what they wish to read or go see. It also is a veiled attempt to ridicule the tastes of the person it is directed at and thus marginalize their opinion that way. In addition, this is designed to indicate that standards for one audience subset are completely different from another (which usually isn't the case in application).
2a) “It's just a kid's book/movie/etc.”
Along the same vein as “not the target audience,” but also insults the intelligence of the target audience.
3)“Not published? Can't criticize!”
People who hurl this one should be warned that you never know who has or hasn't published something somewhere and that it runs the risk of blowing up in your face from the start. Furthermore, there are plenty of people around with degrees who know how to use them even though they might not have been published (all that essay writing does come in handy sometimes). Furthermore, if those who are published have such a vaunted opinion, why should we let them have the power to tell us what to think about a text?
4)“You're being mean.”
Disagreement hurts some people. Other people will take criticism, recognize it as high grade fertilizer and make their stuff better than it would have been. In most cases with regards to books and movies, the “hurt” party (usually the author or filmmaker) can cry all the way to the bank. They have your money, you are free to complain about entertainment services not rendered.
5)Direct insults as to one's personal habits.
These are always best ignored for the lame distraction they are.
6)“It's popular.”
Yes and so were pet rocks, harem pants and absinthe. Popularity and quality do not go hand in hand, nor does it automatically nullify a considered opinion.
7)“You aren't a fan so you don't get it.”
This is rather a mystifying argument if ever there was one. If one isn't a fan and takes a chance on a book from an author they've never read before and finds it not to their tastes, then the reader does get to have their opinion. That a fan will likely disagree with them is a given, but how that opinion constitutes “a threat” is the real puzzle.
8)Rambling about things that are only vaguely related to the topic.
Respond as one will in a pleasant manner. Vaguely related rambling can be fun.
It should be noted that on certain rare occasions one does run into people who will happily debate one's points of opinion. At such times, have fun, get a cup of tea or something and shoot the breeze. ^_^