an armchair critic, traveller, etc.
an armchair traveler
One who speaks authoritatively about traveling despite not traveling often. Don't let him discourage you when he's just an armchair traveler who's never been out of the country!
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
an armchair critic, traveller, etc.a person who knows about a subject only from what they have heard or read and not from personal experience: He’s what you might call an ‘armchair traveller’, having never actually been outside Europe.
See also: armchair
Farlex Partner Idioms Dictionary © Farlex 2017