You and your friend are out at a bar. A mixed group of people are at the table next to you and somehow they include you in the conversation. They ask you both if you want a drink. You both accept and are enjoying the company. Your ride comes to get you to leave. You say goodbye and leave the remainder of the drinks on the table.
It just so happens that you don’t leave immediately. You meet some other people you know and engage in another conversation. The person that bought the drink seeks you out and chastises you for not finishing the drink.
Is this how they do in Houston? What is the rule on finishing the drink that someone else bought?