My grandparents are having a lunch event but I don't want to attend it.
What do you think will happen if you don't attend?
I don't know, I just don't want to be around my grandpa.
It is important to spend time with your grandparents since they will not be around forever. You should attend the lunch event with your grandparents as it will be quality family time together and you won't have many more opportunities to spend time with your grandparents in the future. If there is something that is straining your relationship with your grandpa, discuss it with him so that your relationship is no longer affected.
I'm going to skip the event no matter what you say.
I really think you need to take some time to think on this. Think how upset they will be if you just decide to skip out on it. It would mean a lot to them to see you there.