playnicely I am trying to analyze exactly why it's so irritating too! I think as we are very social animals who have always lived in packs or tribes, on some deep primeval level we need to know that we can work as one, all accept the same conditions even if they are not our personal preference (democracy) and rely on the cooperation of others when under threat. Food is such an important social bonding mechanism for human beings and perhaps We have a subconscious inherent distrust of people who are incapable of pulling together for the greater good and who would appear to put themselves on some sort of pedestal of difference that must be catered for.
It reminds me of the scene in the Royale Family where Nana insisted she needed to have only the breast meat of the turkey because she 'can't' eat the brown meat! Of course she could if she wAs genuinely hungry and in need of protein, she just didn't especially like it in comparison to what she perceived to be the better bits.
If you live in a relatively privileged world where you have never known real hunger and a huge variety of foods are readily obtainable you can easily convince yourself of the narrative that goes 'I can't eat that and it's not my fault.'
Of course you are rarely required to actually put this to the test, beyond touching the tip of your tongue to the end of a spoon and upon immediAtely tasting something unfamiliar or strongly flavoured your brain goes 'No! Lockdown! Unfamiliar taste/substance/texture! Panic mode!' Because you have already convinced yourself in advance that this substance is not for you and there is no real incentive for you (ie real hunger) to actually chew a few mouthfuls and give it a fair crack of the whip. But what it really happening is that you are saying 'I won't and as I am not yet starving I don't see why I should have to.'
Again, on a primeval level, when you are hunting, gathering, cooking and eating as a group and pulling together to make sure everyone gets their fair share according to their age/size and the physical job they perform, and that much needed nutrition reaches those who need it most; the hunters, the fighters, the protectors, the pregnant, the young, weak, elderly and sick, the last thing you have much tolerance for is someone who insists that their taste preferences are more important than everyone else's collective needs. You can't afford to be fussy, you eat what's there because it's all there bloody well is, and fussiness sees you either starve or be extremely unpopular and considered ungrateful in your social group.
Even though those arguments don't really apply to us in the developed world now, I think perhaps that's why on a deeply subconscious level we still find it deeply irritating to be around an incredibly fussy eater.
Most of us have at least one or two things we might gag at or really struggle with. I wasn't enamoured by the sight of chargrilled goat liver and lungs wrapped around a skewer using lengths of intestines on Rick Stein's travels through Albania the other day. I really think I'd have to be on the verge of passing out through hunger before I'd want to eat that, but if I was served it in Albania by someone who found it totally delicious and was being hospitable I would reluctantly chew my way through a couple of mouthfuls and spit it into my napkin when no one was looking because I know it would be important to them (again on some sort of subconscious primeval level) that I tried. And I might even surprise myself and find that is is surprisingly delicious.
It's normal to feel that way about a small handful of very unfamiliar and challenging foods. When you react that way to 75% of the everyday familiar foods around you it's less easy for people to be understanding.