Words and idioms for someone who loves to sit in judgment of others

What single words and idioms would best describe someone who loves to sit in judgment of others, almost making it a hobby to become a nitpicker. They are aware but un-acknowledging of their own deficiencies and of their non-eligibility as critics. They are overly critical of others, yet vehemently intolerant of any criticisms directed to them. I guess it is a combination of spite, rudeness and lack of insight. But they are not stupid.

As examples you could imagine an unaccomplished reality TV judge (I’m not sure what credentials they possess) being spiteful and mean. This may not be a very good example because sometime the judges put on a veneer of [this attribute] for ratings? Or say a colleague at work who feels threatened by your skills? Or a meddlesome neighbour perhaps who is jealous of your success?

Edit: Having considered the responses so far one apt overarching word I think is hostile, but perhaps there are better words or idioms? Another word that applies perhaps is caviling.

Solution 1:

Such people could be called armchair critics.

An armchair critic is someone who offers advice but never shows that they could actually do any better.

Solution 2:

Maybe this should be an answer after all:

Given your comparison to reality show judges; if you are thinking of a particular such judge, create an adjective from their name, as in Sternian or Mandelian or Cowellian.

Solution 3:

Sneering can have this meaning when used to describe a person or people - a personality inclined to sneer at others.

It implies spite and scorn - hostile, contemptuous unjustified judgment and a sense of assumed superiority. It also that the person judges others because they enjoy spiteful judging.

A few examples from the press:

Sneering TV talent-show judge Simon Cowell...

Why sneering reality television is as bad as the Roman amphitheatre

The Real Romney Captured on Tape Turns Out to Be a Sneering Plutocrat

Keith Kloor lumps me with Dawkins as sneering, strident, and...

Since it's an adjective and Shyam's suggestion is a noun, you can combine the two. "Armchair critic" implies inadequacy, and "sneering" implies spite.

I can't stand these sneering armchair critics who judge talent shows.

(just be careful you're not sneering or an armchair critic yourself when criticizing those who are!)