At a party/gathering, people are served drinks in identical vessels (childrens cups, beer bottles, wine glasses . . .) and it is very difficult to determine whose drink is whose. Mark cups, glasses, and bottles with the drink-marking device (special purpose drink marker) to identify drink ownership. And when the party is over, apply cooking oil to marks 5 minutes before cleaning/putting into dishwasher for a mark-free glass that is ready to use at the next party.
