Putting out coasters for your guests is a great passive-aggressive way of telling them that you don’t appreciate drink rings. But if you have friends who may not respond to subtlety, you might want to consider Indelicate Doily Coasters.
Each coaster comes complete with a hard lesson in etiquette, such as “Don’t Stain My Table, Douchebag” and “Be Considerate, Bitches.” The doilies come in a set of 8. However, your number of friends may decrease after using them, so order accordingly. Available here.