First, who are all these people telling others that they will only be good for flipping burgers (as if burgers don't need flipping?)
Secondly, one sad truth of life is that we all have memories of someone saying something to us (off the cuff often, shooting for the hip) that stays with us for life. It can be a bad joke from a loved one, a friend or a teacher. It can even be an action, or a disgruntled sigh. Something that can grow out of proportion and stays with us because it made us feel so separate from them or not acknowledged, while the other will not even remember what they did*. (We can do it to another person as well of course).
My point being: it's not unique. So when someone on Twitter asks about it, they will get plenty of stories.
*Obviously I am not talking about actual abuse or bullying here!