I don't think it's ungrateful at all to reject or refuse food.

Yes, I have mentioned it in my post:

Are they ungrateful? No, not even the tiniest bit

I agree.

I also am not fond of quite a few things. But having said that, being the one preparing and managing food for the family now, I get quite irritated if they can't seem to have common liking...

So I try to blackmail them into eating whatever I have prepared. Of course I take care of their preferences. So yeah ;)

The blackmail seldom works. Most of the time they manipulate me into making something else for them. Not that I mind too much. But then it's toast and cheese or toast with chocolate spread! Not a whole new meal :)