@futurebird
In my case it was being "too tall" and skinny. However, I think that if it wasn't that it would have been something else due to my general social ineptitude and inability to stand up for myself (and turning down the boy who bullied me).
I'm not trivialising it, or victim blaming, it set me back years in self confidence and ability to get on with stuff, but bullies prey on the weak and if it's not gender norms it will be something else.