Anything and everything 
In primary school - for not having the best branded clothes/track suits/shoes (no uniform).
In secondary school - for being too quiet, so I got louder then was bullied for being too loud.
For being an easy target - so I toughened up a bit then was bullied for having a temper.
For opening my mouth to speak.
For sitting quietly with a book, pretending I wasn't too scared to speak.
For being polite to teachers - so I started smoking/bunking off/mucking about, then I was bullied for "trying too hard to be bad".
For being shit at PE - the PE teachers used to join in with that as well - throwing netballs and footballs at the backs of my bare calves when they were stinging with cold and rain, telling me if I was running faster they wouldn't be making contact.
For being fat/ugly/unfashionable - yeah I probably was a bit, but perhaps this was all due to the self-confidence issues I had as a result of being bullied...
For not being attractive/slim/fashionable enough to attract any of the boys - so I put out, and was bullied for being a slag.
For self-harming (apparently this was nothing to do with all the bullying - I was "attention seeking").
I remember one of the bullies leaving in the first year to go to another school - the feeling of relief was immense but short-lived as one of the other bullies said there was a new boy starting in her place, and they would tell him from day one that if he wanted to be on the football team he'd have to bully me too (so, of course, he did...)
In adult life, work and relationships... For setting a precedent by trying too hard in the first instance, burning out and being unable to keep up the ridiculous level of effort I try to put in, and subsequently being branded as "lazy" because I just cannot keep up the pace (which, I might add, is significantly more than the majority of people could ever manage on a good day 😒).
And sometimes I wonder why I feel angry, frustrated and useless...