Yoshi, do you have a stepparent? I wonder if any of the previous posters do.
I have a step father whom I absolutely love. He is a wonderful addition to the family and makes my mother so happy.
However, he came into our lives at an opportune time. All of us were already out on our own. He didnt try to be a “parent” to us, just my mothers husband. We have great respect for him.
If your stepparent is interfering with your relationship with your biological parent, I could see how you might want to hurt your step parent. Just keep in mind – you dont want to create a rift between you and your parent OR between your parent and step parent. Its a sticky situation.
I dont know the halachic answer, but I cannot imagine that hurting your step parent is as severe as your parent. BUT, none of us really know the stakes…