Etiquette is for everyone. Etiquette isn’t just for wealthy country club types (although we all loved Thurston Howell III).
Money, social standing, and or brains–no matter which you are lacking, good behavior levels the playing and smooths the way between two people.
Manners such as using the correct words in a sentence, waiting to be seated, and having good posture can make a difference in how you are treated by friends, co-workers, family, and neighbors.
You can’t buy manners. It doesn’t matter what your parents do/did for a living, how much money you make, where you live, how you were raised, etc… The rules of etiquette have been catalogued in books, magazines, websites, and on YouTube videos. That being the case, excuses for not knowing how to behave are just lame and lazy.
Good manners are a valuable asset and cost nothing to acquire.