After lots of flying into/out of the US, plus many internal flights there, I've noticed they have more of a culture of bringing food onboard.
I used to think it was really rude, but over time it bothers me less. And given the food quality on some flights, and lack of choice for fussy eaters (me), I do understand why people do it.
I would console myself that, being in F, you're not in arms reach of the food and having to resist saying "are you going to finish those fries?".
I made the mistake, when a youngster of about 23 years old, of taking a chippy onto a rush hour train once. I was not popular, as everyone was on their way home for dinner and I had reeked out the whole carriage. Lesson learned.
But I wouldn't be upset about a McDonalds on a flight - better than the usual smell of BO and farts. Which I've apologised for, but people still don't like.