opinions are like assholes

Etymology
Shortened from "Opinions are like assholes; everybody has one"; "Opinions are like assholes; everybody has one and they usually stink"; "Opinions are like assholes: everybody's got one, and everybody thinks theirs smells nicer than everyone else's"; or some variant of the three.

Proverb

 * 1)  Everyone has opinions, and most people's opinions are of exceedingly poor quality.