Was i wrong for doing this.?

my grandpa is very abusive to everyone in the family. I have been away from the whole family for all my life just about because of his abusivness. We came back to the family because my grandma had cancer, and pluse my grandpa found God so to speak. He gos to church and has his own friends at church. But he chooses them over his own family which he has abuse. So we were gonna go to a movie and my mom was gonna pick him up we were almost their and he starts bashing about the Bible and God. My mom told him to stop about 6 times.. He started getting out of controll calling my mom a slut and all this other bullshit. So i said to my grandpa, you need to stop. He turns around facing me and hollers out. "IM GONNA CRACK YOUR FACE." So i pull a knife and said do it i'll stab the **** outta you. my mom pulled over and kicked him outta the car... is that what they call courage?