What do you think of me skipping my grandma's birthday?
What do you mean by 'skip'?
I want to go somehwere else
You should at least make an appearance to important family functions. It is wrong to miss them if you don't have a good excuse.
I have a good reason to skip her party, I have a date.
You never know how many birthdays an older family member has left, so it's really not wise to skip out on the celebrations. See if it's possible to move your date to a later time or different day, so that you can attend both. You're grandma will be very pleased to see you at her party.