I don't want to attend my sister's engagement
Why would you miss such an important event?
I just don't feel like going at all.
It is a special event for your sister who expects you to go even if you don't want to. It is quite a milestone for her. Something she will have to be there for you to go to as well. We all have to do things we don't really want to do.
If my parents want to force me to go, I make sure to make it the worst day of their life.
I think you might like it if you go, and even have fun. At the same time your sister won't forget you did this for her, and will always reciprocate. Tantrums are looked down in public by grown people.