Any opinions that disagree with a priori facts are wrong. An a priori fact is something that is true in itself. Using the current laws of language and mathematics, "a square has four sides" is fact. "In my opinion, a square has 3 sides" is simply wrong.
However, opinions can also be morally wrong, though this is much more difficult to gauge due to (in my opinion - ho ho ho) there being no objective moral values. However, society determines morality, so if your opinion that killing babies is hella fun and should be done at all available times goes against the collective morality of society, then it could be said that your opinion is wrong morally.