What's the word for "someone that doesn't know something but pretends to know it?" [closed]

This guy thinks a person is arrogant when he knows nothing about that person and just telling everyone about how arrogant that guy is. So what is the term for this kind of person?

Solution 1:

swank

behavior, talk, or display intended to impress others.

posture

behave in a way that is intended to impress or mislead others.

pretentious

attempting to impress by affecting greater importance, talent, culture, etc., than is actually possessed.

know-it-all

a person who behaves as if they know everything.

smart-aleck (ass)

irritating as a result of behaving as if one knows everything.

Solution 2:

Perhaps a bloviator? Oxford Online defines bloviate as

Talk at length, especially in an inflated or empty way.

Similarly, windbag

A person who talks at length but says little of value.

Oxford Dictionaries Online

Also gasbag

One given to empty or boastful talk.

American Heritage