When one eats in excess, claiming he or she "forgot" how much they have eaten
Chuck: Who ate all of the cookies?
Guillermo: I only had 3
Chuck: I'm pretty sure you ate them all beacase you were the only one here when they were eaten, it appears you have food amnesia
The act of forgetting the food one has just previously eaten, made famous in an episode of Spongebob when Patrick Star eats his own food and forgets soon thereafter. This can also lead to accusing other people of eating or stealing ones food.
Terry: Where da fuck is my sandwhich?
Nardo: The one you beasted on, like five seconds ago?
Terry: No, I didn't even take a bite yet!
Nardo: Bro, you have a case of food amnesia
This happens when you've just eaten something like... 2 seconds ago... and forgot you ever ate it.
Patrick: Where'd my candy bar go?
Spongebob: You ate it, Pat, it's all over your face.
Me: Major food amnesia
Angel has serious Food Amnesia. She JUST ate that apple core.