The difference between you and someone else is just home training.
We should learn to accept others the way they are because we all are not of the same family background.
The same reason the number 9 looks likes the number 6 to two different people opposite each other is just the same reason why we should not judge.
At your home you may have been told not to eat somewhere else but the dinning room and to someone else eating in any part of the house is normal,and when such a person comes around you, don't see him as uncultured or ill table manners.
We all are just perfect in our imperfect ways of life.
Over the week i saw how a mother was talking about her son's new behavior of constantly sleeping on their couch...and i asked her when it started and she replied that ever since the young chap came back from his holiday at his best friend's place...and i laughed and told her that it could be that where he went,they sleep at their couch always..so lets just accept everyone the way they are.
GOD bless you