Parents come from a different generation and generally have their own way of doing things. Sometimes, "their way" includes embarrassing their kids with behavior that just doesn't fly anymore.
Maybe you went grocery shopping with your mom and she tried to use two coupons, even though both coupons stated they could not be used in combination with any other discounts. When the cashier politely declined and said she could only scan one, your mom went ballistic and demanded to speak to a manager. The manager came over and told her the exact same thing.
Or maybe you were at a restaurant with your dad, who seemed set on making your dinner a living hell for the waitstaff. He'd snap his fingers at the servers when he wanted more to drink, and he sent his dinner back because of a "mistake" that was actually due to his own inability to properly read the menu. You were mortified.
Or, heck, perhaps you've got a grandparent that takes the cake for entitlement. Maybe you once went to a play with your grandma, and she refused to turn her phone on silent "in case she got any messages" and would check her phone, brightness all the way up, throughout the show. You asked her nicely to stop, but she insisted she was doing nothing wrong.