I'm mad my GF wouldn't thank my dad for his service at a dinner honoring his service
That's interested. What kind of service was he in?
He was a member of Knights of Columbus
It is wrong to be angry with your GF she might not know what a knight of Columbus is. If you are so offended you should not be together and break up.
It would have just been nice if she has acknowledged it.
Well you seem to care a lot, so why not just tell her how you feel instead of being angry? She doesn't deserve you yelling at her for such a petty reason.