My wife used to say it (eat someone's lunch) used to happen a lot where she worked. I don't get some people
I don't get that either. First of all, it is extremely rude. In the animal kingdom you could get killed for that. I also am sort of a picky eater so I wouldn't even think of taking someone else's food. Unless they want to share and tell me what's in it.
Which reminds me of a long-ish anecdote I want to share:
I once worked in a factory, 3 shifts at our production line.
A shift was a team of 3 people, but we could do the work with 2 at slightly reduced production. One of our coworkers always liked to take fridays off. So it was usually me and the other guy, who I got along with very great.
One friday my coworker brought in an entire leftover pizza from home. He said to me: take a slice... or however many you want. It was nice pizza for being cold. From there on it escalated every friday.
Our ongoing "prank" was: "to fatten your coworker up". Luckily the other guy with the usual friday off was constantly on a diet so he didn't miss out. Next time I brought a pizza. Then we brought in various snacks, fruit, cakes, pies, potato chips, subs, etcetera.
We were good friends so we knew what the other one liked for the stupid "prank". It got so ridiculous that we couldn't get it all on the little table and in the little fridge at our station. During the shifts we often had to call other stations to come over: "hey, we got sausage rolls, come and get them." And to the shift after us: "we got you guys breakfast".
After 6 weeks or so I had to concede. He won.