You can only coast for so long on the "whatever" wave when it comes to eating. Because you need to eat every day, several times. It means nothing during a dating period (or courting, if you're fancy like me). That's the time when you go to a restaurant and you pick your arbitrary choice from a list and someone else makes it. You'll both have the pig liver in chocolate sauce, sounds great!
When you've settled in to a relationship, the gloves come off. When they were putting their best foot forward by being agreeable to anything before, now they just want to be happy. They want to eat a whole pizza to themselves, or toast for four days straight, or they need the kid at McDonald's to make them a burger with three pickles, 22 onion pieces, a dab of vanilla shake in the center of the ketchup, and all the fries need to face east. It's at this point you start thinking "What the fuck side of a fry is the face?"
It's not so much the individual food choices -- a passion for Hot Pockets or ketchup on a steak -- it's that this person is now showing a side you've never seen before, and he or she is coming across as if nothing is ever good enough for them. Your effort is wasted and they don't respect the time or work you put into trying to make them happy, to engage in what a lot of people consider one of the most basic and obvious forms of caring for another person: nourishing and feeding them. Instead they shit on it and wipe their ass on a corn dog, which is not how corn dogs work, let me assure you.