I'm not going to a wedding
Is there serious issue going on? Do you have other plans that day besides the wedding?
Yes, I have better things to do.
They invited you to their wedding and it would be rude not to go. Unless your other plans are very important, you should prioritize the wedding.
I'm going to get high, drink and hook up with other women at the wedding.
That would be horrible behavior at a wedding. Either way it sounds like you are trying to let down your family and it would be better if you could be supportive of this wedding.