I'm not going to let my little sister get a giant llama plushie
Why are you not going to get your sister a giant llama plushie?
Because I have a plan for her. One day, when she is in a terrible mood, out of nowhere I'll wake up with a huge slap on the cheek.
Why would you keep her from getting what she wants, and abusing her after? How do you think she'll feel after her big brother treats her like that?  Wouldn't it be better to give her the plushie and see her happy with a big smile on her face?
Hey I was just kidding. I care about her and I want her to have a good day.
I am glad you were just joking around. It is fun to goof around with your siblings as long as it is harmless.