This expression was very common in my village and it was the short version of the sentence ‘The frying pan said to the pot, don't tarnish me’ which means that a person cannot criticise another person for something in which he is not an example.
Undoubtedly it has its roots in the biblical phrase ‘And why beholdest thou the mote that is in thy brother's eye, but considerest not the beam that is in thine own eye?’ which through time and cultures has mutated and been compared to other popular things.
Destructive or ironic criticism of other people's mistakes is commonplace in human beings, instead of advice on how to prevent this from happening, and although big cities have dulled the scope of this criticism, the modern media have managed to viralise it.
Respect has been diminishing and the common situations that I experienced in my childhood no longer exist, the young son of my neighbour when he addresses me he does it as if it were to another of his age and the rules have been disappearing in the big urbs, although they are reluctant to disappear in the villages.