It's not ideal to use expired vinegar although it is technically safe to eat. The expiration date on the label refers to the flavor and quality of the vinegar, not its safety. In reality, vinegar last indefinitely and can be used if there are no spoilage signs present. However, its acidity decreases over time so it will become less potent. Also, make sure your vinegar doesn't contain perishable ingredients such as herbs and garlic. In that case, it's best to use the expiration date as a guide.