Foreign workers deserve much more respect. While we may not be able to do much at construction sites and homes, there is no reason why we should stand for it at public facilities (Treat foreign workers with respect; March 2).
I have noticed that if we direct an innocuous question, such as "What is wrong?", at the service personnel who are being rough with a foreign worker, it works well.
He may have a genuine cause and explain to you. On the other hand, he will tone down immediately because the treatment being meted out has been noticed by you and made aware to others waiting with you.