I'm going to refuse to go to the funeral of my gf's dad
Why refuse to go to the funeral.
He was such an asshole
Even if you don't like the guy, you should go to show support for your girlfriend.
Nah, I will just make up some stupid excuse and stand outside during the service having a smoke instead.
That is very disrespectful to her and her dad. Just go to the funeral. Sometimes you need to do things you don't want to do for people important to you.