As I explained in The Nine Most Common M.O.s of Irrational People, regarding know-it-all’s (which also applies to opinionated people):
Know-it-alls like being the only expert on any topic, even if they’ve never “been there” or “done that.” They will find cracks in any idea you offer, even if it’s correct. They know that if they can make you feel stupid, you’ll lose confidence and often back off and become submissive. Their M.O. is to belittle, mock or condescend to you.
And your immediate reaction?
These people may make you feel small, insignificant, not good enough, and sometimes ashamed—as well as resentful.
In reality, there are three kinds of opinionated people. The first two are truly offensive, whereas the third is just obnoxious: