Stress (or good involvement in something) can make us forget to eat. I keep around lots of fruit, yogurt, and "easy" things to eat, hard boil eggs, etc.

Depends on who was telling me I didn't eat enough as to whether I paid attention. I'd probably look at their "motives" for what they were saying. Some mothers would probably never think their child ate enough :-) but good friends whom I trusted or theapists/doctors, etc. I might look harder at what I ate to see why they thought that.