I have a new one - after this Thanksgiving.
If you say you're coming "for dessert" - either eat it, or take it home with you. Don't put us to the trouble of making a lot of stuff - enough for MIL, DH, and I to have a small serving apiece, with plenty left over for the four of you - and then refuse it.
We had baked 2 apple pies from scratch, laid in some whipped cream, I made my famous "Pink Stuff", and MIL brought over a half gallon of ice cream to go with the pies. We three had dinner around 3 pm.
BIL and family showed up at around 7:00. They stayed for about an hour - and turned down the dessert, because they were "too full" after having dinner at her sister's. No, they didn't take any leftovers, though they were offered.
Did I mention that I'm both diabetic and obese? And that MIL and DH are both carefully watching their weight? And that BIL & family (all beanpoles who have trouble keeping weight on) know this?
I also learned this: If they can't tell us whether or not they are coming until the day before, I don't need to cook for them. Yep, we bought enough food for 7, only to be told they would come "for dessert," and then they didn't even eat that. Can you tell I'm resentful? And they are great people, not moochers, not toxic or any of that stuff.