Kibitzer: someone who offers unwanted advice; someone who offers unsolicited opinions 

Kibitzer is a Yiddish word.  Originally, a kibitzer described someone looking over your shoulder during a card game, offering unwelcome advice.   These days, a kibitzer is an outsider offering unwanted advice.   

Ultimately, kibitzer likely comes from the German name Kiebitz.  The Kiebitz is a bird with a reputation for being annoying. 

When it comes to using this word, I’d give you some advice.  But, you didn’t ask.