"Fasting is so hard, I don't know how you do it" is what they often say. Or "I don't understand how you eat so much, but don't get fat".
Meanwhile, they don't realise fit people workout daily and eat good the majority of the time.
Discussion
I think part of the problem with these types of people, is how they do not hangout with fit and healthy individuals enough, so their perspective is skewed.
For example, when I see old friends who are chubby, it will be at events. We'll have a dinner, a kid's birthday party, ect. So they'll see me eat food I usually don't eat, and wonder how I don't look like them.
They don't see me working out daily. They don't see me typically only eating between 2-7pm. They don't see that I typically only eat food that can be killed, plucked or picked. No preservatives or package foods.