Country Dictionary

a crazy, aggressive fucking fire-crotch of a disturbed family

I'm going to beat your ass like a red-headed step child.

A stepchild might be singled out for abuse. But a red-headed stepchild (who presumably looks like his or her absent birth-parent) might be abused even more because he or she is so obviously different from the other children.

Myles was the red-head step child of the family, he was never invited to the family reunions.

an unwanted, (ashamed of) child. Less than desired child

Mike was the red headed step child of the family, treated pretty shabbily.

A bashling. Some one who is singled out for emotional abuse and/or physical abuse. Some one who gets purposely written out of their inheritance. Some one with no birth rights. Some one purposely neglected financially. The unfavored one.

In my father's family I was just a red headed step child.

Derives its meaning from the idea that;
1. Red heads are to be avoided
2. That step children are to be avoided.

So the idea of the both combined is doubly hateful

"beat him like a red headed step-child"

someone that is beaten every day by their father that is always high as balls.

a teacher see's a student after class because she had seen the bruises. she ask's him what happened and he said im a red headed step-child.

a tired simile meaning to beat badly. A fresher phrase would be to "beat like a fat kid stealing lunches"

The prosecutors got beat like a fat kid stealing lunches.