As someone who’s weight has dramatically fluctuated over the years I can tell you I’ve gotten shit for being too thin and for being too fat. In my experience it is definitely way worse and way more constant to get bullied for being on the heavier side. When I was picked on for being thin it came off as much more of an envy thing too, (which is depressing, because I was bulimic and actually really unhealthy) whereas the treatment I have received while being on the heavier side is incredibly demeaning, judgemental, and cruel.
Oh, and incidentally, in the city I live in a woman was followed home from the store last wee and yelled at to lose weight, had garbage thrown at her, and was physically attacked by 6 men. They made it very clear that the reason for this was that they thought she was fat.
I’ve never heard of someone experiencing this level of hostility for being “too skinny”.