That used to be the case when my MIL's sister and her family would come over for dinner. They haven't since about the 3rd year we were married though.
They would come in with several tupperware bowls, and before dinner even started, they would fill them up with what they wanted to take home as 'leftovers'. Then before prayer, they would jockey themselves to where they would be in the front of the line, and would pile their plates so high, they could barely balance them. Then they would sit down and eat fast so they could get up and get seconds of whatever was left, as soon as the line cleared. I never could understand why nobody said anything to them. It was like they were afraid of them or something.
The last year they came, it was same as usual. The only redeeming factor about any of them was my MIL's sister, Ann, would ask if anybody else wanted something if it was the last portion before she got it. That year, every time she asked, I said I wanted it. After the second time I answered her, she said, "Lord, you're a pig aren't you?" I told her, "Nah, you can have it. I'll just get what I want out of the bowls you put in the fridge." Michele's mom's mouth was hanging open in surprise, and her dad looked at me and winked and smiled.
There were two babies born soon after that, and Michele's brother got married, so the family had grown by the next Thanksgiving. When Michele's aunt called the week before and asked what time dinner was going to be, Darrell told her that it was only going to be immediate family. She called for 2 more years after that and he gave her the same answer. Guess she got the idea, because they didn't call anymore after that.