How 'bad' can a backstory be?

Quick question in regards to the 3 - 1 - 3 rating; are characters allowed to have terrible pasts involving parental abuse (NON-SEXUAL)? Or is that too much ;-; (i was just catching random chars backstories and wondered how tragic people got with them. I don't want to be the outlier and have a story thats horrific when no-one else has one :P).

Thank you!