My friend makes me so mad, I want to shove him!
Wow, why do you want to shove your friend?
He once threatened me with a knife.
Threating someone with a knife is very serious, but shoving them is not going to solve anything. How long ago did this happen? You called this person your friend, so surely you have forgiven them for past poor behavior at this point.
He wouldn't go through with stabbing me. He's just annoying.
If he keeps up with threatening you, you should probably leave. Even if he doesn't really mean it, you will lessen the risk of injury if you just leave the situation.