I have a picky eater, well two really. There is a very limited amount of things my son will eat. He's always been like it. Getting him onto solids when he was a toddler was a nightmare. I've done everything 'right' so to speak, never cooked an entirely separate meal, he's always had to at least try things before he screws up his nose, etc..... He's still shockingly picky and if he doesn't want to eat, he just won't. No threats or bribes of desert, going to bed hungry or loss of tv time will work.
He recently had a sleep over at a friends house. I think the mother thought I pandered to him a bit. She's also heard me lamenting about how tiny he is, so I think she decided in her head that she was going to get him to eat. She rang me at about eight o'clock to apologise because son had gone to bed after eating two bites of a sausage roll for tea. She was astounded. She said, "he ate two bites and then said he didn't like it. He asked politely for something else & when I said no, he just nodded and wandered off! I offered him an ice cream if he ate more, I told him I'd turn the tv off, I said he wouldn't be able to swim in the pool tomorrow & he knew I meant it, nothing worked!" I was roaring with laughter at this point. I said, "I did warn you. If he don't wanna eat, he aint gunna!"
It's very frustrating and his father is very much the same. They're both identical builds too. Muscly and fit as all get out, but without an ounce of spare flesh.