🕳️ Donatello's tastebuds are highly sensitive to all kinds of spices and ingredients. Yes, the ability to tell what's in a dish is useful... but it's more useful to detect lactose when you ordered lactose-free, tell apart cola zero from regular cola, and taste harmful bacteria. He can't exactly explain how or why, but he can taste when something will make him sick. It has a very distinct flavor to him, and it immediately causes saliva to pool in his mouth. He's rather picky with what he eats, and listens to his body's signals when he feels the familiar flavor spreading on his tongue - why should he swallow something if his body wants to reject it? He'd rather starve than eat food that will disagree with him. He'd rather eat something he doesn't enjoy than something heavily processed. If his gut bacteria is happy, so will he be.
🕳️ Of course, sometimes he simply doesn't have another choice. Donatello doesn't exactly have a lot of money, and there are times in which robberies don't go well, and he simply can't afford to be picky. While he's fine with going hungry for a day or two, he had to endure starvation and illness in his youth, a near death experience even, and he definitely doesn't want to repeat that. Bad food is better than no food, even if it gives him horrendous stomach aches. Donatello can feel every single thing that's going on inside him. Most of the time, the usual, idle digestion doesn't bother him, but indigestion of any kind has the potential to make him extremely uncomfortable. Nausea, heartburn, gas, or even food poisoning legitimately put him in a position where he can no longer function. All he can do is freeze like a deer in the headlights when his insides start rebelling, so he doesn't crumble into a million pieces...
🕳️ Because of his high sensitivity, Donatello isn't a fan of being starved, or being fed, or giving anyone else control over his food intake in general. You'd have to be very lucky for him to allow you to feed him just a small spoonful - probably of a meal that he picked himself. Vulnerability is a big no-go, and that includes having his stomach touched, or even just seen. It's fine when a doctor does it. It's fine when it's an accident. But once again, if your hands are anywhere near his belly for longer than two seconds, he freezes like a deer in the headlights. All of a sudden, he's 15 again, on the verge of dying, and some inmate is punching his already aching stomach. He doesn't show just how much just a light touch to his belly can set him off, all you can see is that he's sweating and trembling ever so slightly.
🕳️ Oh, but Donatello would be such a sucker for a good belly rub, if only he allowed himself to be... with his heightened senses around his insides, it would be an almost orgasmic experience, honestly. Whenever he gets aroused, he first feels a familiar twinge around his belly button... His middle is a highly erogenous zone for him. Perhaps that's part of why he doesn't want anyone to touch it. He'd never tell anybody, but sometimes even just touching his own belly makes him blush... hearing and feeling his own stomach growl causes him to sweat... overeating and drinking carbonated drinks too fast makes his heart race. Perhaps his brain doesn't quite know how to deal with the hardships he had to endure in the past. Perhaps, in order to deal with his own discomfort and vulnerability, he ended up developing a fetish for this kind of thing...
🕳️ I doubt he'd be an obvious tease... Honestly, I don't think he'd ever be comfortable playing with his belly in front of you, or dirty talk. But he would tease you with a stone cold resting bitch face, explaining in great detail how he can feel air and liquid shifting inside him in this very moment. He'd get close to your ear, asking if you want to know his opinion on something - and let out the airiest, longest burp you can imagine. And he'd certainly make direct eye contact with you while he eats your snacks, simply because they're "better for him". One thing he can't cover up with his cool attitude is when his belly gets noisy, though. He averts his eyes and starts stammering, trying to cover it up with a pillow or by drinking something... no, it usually doesn't help. He just gets very, very embarrassed.