Weird! I noticed this about a skinny friend on mine, Sara. We were standing in the kitchen eating one day and she took a bite of a oreo and then emphatically threw the rest of it away.... I had noticed this behavior before but I hadn't said anything. FInally I said, "Why'd you do that... throw the oreo away?"
She said, "Because I only needed a bite."
She didn't care that it cost money, looked silly, or if it was a bit unconventional. It's amazing how many times you will eat something, THE WHOLE THING, when we don't like it, didn't care for it, were FULL or if it was bad. It's some screwed up mentality! Now, I make waiters take stuff back that I took one bite of and said YUCK. Or, like Sara, if I only "need" a bite of an oreo, a piece of cake, a doughnut, I take that bite and throw the rest away (immediately), not caring how much money it cost or if I'm wasting (instead of waisting) food.
Anyway, it's was one of those tips I stole from the skinny girls.