I'm going to cuss out my sister in public
Did she do something to deserve being cussed out?
No, I just feel like shit and it'll make me feel better.
Are you sure that is what you want to do? It is going to hurt her feelings if you cuss her out, especially in public.
I'm going to do it anyway.
I really think you should reconsider. It's not only inconsiderate to your sister, but inconsiderate to the other people around who have to listen to you.