This actually happened 15 yrs ago when I was married to my first husband, but I've run into similar things since and I'm still not sure of how to be polite.
Anyway, my 1st DH (Tee) was a big man- 6'4" and 250 pounds. He ate like a horse, so I was used to that. I'm also big- 5'8" and heavy, and I like to eat. But a family of his friends took the cake (and a pie, and some cookies...)
The first time we ate with these friends, and their 17 yr old daughter, I was unprepared. The Husband was already over 500 lbs. and Daughter was close to that. Wife was in the 200's. Wife asked us if ordering pizza was ok, and what we wanted on ours. So far no prob. She went into another room and placed the order. Remember, there are 5 of us eating.
When the food arrived at first I thought some was for later. There were 3 extra large pizzas, one medium pizza, 2 steak hoagies, 4 loaves of garlic bread, and 5 2-liters of Coke. We sat down at the table and wife set up the food.
Husband and Daughter each took 1 extra lg pizza, 1 hoagie, 1 loaf of garlic bread, and 1 2-liter. Wife hands Tee and me 1 extra lg pizza, 1 loaf garlic bread, and 2 2 liters. She takes medium pizza, 1 loaf garlic bread and a 2-liter. Husband, Wife, and Daughter proceed to each take their entire pizza (which she has ordered uncut for this reason), fold it over and hold it in their hands like huge sandwiches and eat the entire things. Husband and Daughter follow with the hoagies and garlic bread while Wife eates her garlic bread. All three pour their entire 2 liters into bucket size steins and drink with straws.
Tee and I eat our pizza in slices on the offered plates, each taking some of our bread loaf. We poured our drinks into the normal size glasses she got us. I had a horrible time even getting down the 2 slices and piece of bread I ate, because their eating habits actually made me ill.
They didn't have bad table manners (ok, folding a whole pizza is not good) in general; it was just the sheer amounts of food eaten made me ill. Going out to restaurants with them was the same- Dad and Daughter would order 2 entrees, 2 appatizers and 2 deserts each, and wash it down with whole pitchers of soda. I finally had to start "getting sick," or "having to work" when plans were made for dinners together, just so I wouldn't make them feel bad by accidentally letting my face show what I felt about their eating.
How do you handle it politely when someone gorges around you?