Can I genuinely dislike my own family?
Why do you dislike your family?
They're annoying and I'm going to tell them how much I hate them.
It's inconsiderate to tell your family that you hate them. If you don't like them then you should try to avoid contact with them, but saying that you hate them is only going to make them upset.
I was only joking.
Well that is an unfunny joke. I hope you do actually love and care for your family and treat them with compassion.  Family should have the utmost trust in you and you in them, so look out for one another.