Food safety and freshness are very important. McDonald's Pineapple Pie has been left at room temperature for a day after it is safe to eat. Microorganisms grow quickly at the right temperature, especially for foods that contain moisture. Prolonged standing increases the risk of bacterial and mold growth, which can lead to food poisoning or food spoilage. To ensure food safety and avoid the risk of food poisoning, it is recommended to follow the food safety guidelines of keeping food at appropriate temperature and consuming it within a reasonable period of time. If McDonald's Pineapple Pie has been sitting out for a day, it is best not to consume it to protect your health. If you are unsure of the freshness or safety of the food, it is best to follow the principle of caution and choose to throw the food away rather than risk consuming it.