Alcoholic man

On the same Friday night, a table of 2 Arabic men spent some much on alcohol. One of them ordered a double gin and tonic and he said it tasted like single. He must be an alcoholic. So, I gave him a double double gin. They are friendly and nice people, they spent good money and of course, I was expecting something from them. At the end of their meal, they paid and after, they started to look through every single details of the bill. One of the men closed the bill folder without putting any tips in it. I was disspointed and when they left, I didnt say bye or thanks to them. But I was wrong, I found £20 tips in the foler for me. I felt happy and guilty at the same time because I didnt thank them when they left.