First of all your motto is to attract many  and diversified customers not only Nepali.
Know and teach what is "customer and how you serve them" and we are bias on the color skin and we think it is okay to show tantrum/attitude to Nepali customer. Man you not charging differently than the white color customer, do you? You are not in Nepal but in TX, change your attitude.

Yes, you want to push sell coke or other beverages because you will be making money, but go to other restaurant ask water and what they do? Do they serve you from the tap then all restaurants uses tap water still  you can upgrade and may cost you 5 - 10 cents per glass ( if bought in bulk) but you can make it if that customer comes with his family or friends, think you made extra bucks there. What if s/he does not visit , O additional profit and bad advertisement vs free advertisement.

Customer services must not be poor, it is the second most reason to revisit your restaurant after the test of the food you had served.

I would not visit again if not treated as other customers and you can not complain you not making good money. SERVE BETTER FOOD WITH EXCELLENT CUSTOMER SERVICE, RESTAURANT ENVIRONMENT CAN NOT BE IGNORED.