Literally did it on impulse without even thinking about it so I wouldn't chicken out, so I blurted it out.
I said "I'm bisexual. I like both men and women. No more anti-gay stuff from you, ok?".
He said, "oh go away, you don't know what you like". I think he'll understand eventually, he needs time to think.
EDIT: Showed him this thread.
I said: "Look, this is what I said to you, these are my online friends who are happy for me that I came out as bisexual."
He said: "Oh you don't know what you're talking about, you've never had sex with a man or a woman before, until then you'll never know."
And yeah, I am still holding on to my v-card at 26. I was insecure about that years ago in high school, but I'm honestly glad I've waited to mature first.
Ask your dad if he's had sex with a man to determine whether he is straight or not.
That's what I did, but he changed the subject. He'll think about it and understand it eventually, he's a boomer with all the associated brainrot so I guess he needs it to be personal before he develops enough empathy to understand.
I hope so comrade. Wish you the best of luck with that.