kibitzer

kibitzer \KIB-it-ser\, noun:

1. A giver of uninvited or unwanted advice.
2. A spectator at a card game who looks at the players' cards over their shoulders, especially one who gives unsolicited advice.
3. A person who jokes, chitchats, or makes wisecracks, especially while others are trying to work or to discuss something seriously.

Your mother's heart, dear, will mend with the advent of children, and her father's father, a wobbly kibitzer pointing to Kat's mom and muttering, A beautiful strawberry girl, why all the fuss, why all the disunion over a strawberry girl?
-- Peter Orner, Love and Shame and Love

Bronzini looked on, sitting in when someone left but otherwise a kibitzer, unmeddlesome, content to savor the company and try the wine, sometimes good, sometimes overfermented, better used to spike a salad.
-- Richard Russo, Underworld

Kibitzer entered English first in America in the 1920s. It comes from the Yiddish word kibetsn (equivalent to German kiebitzen) meaning "to look on at cards."