Kurt is no longer afraid of Karofsky. He even asks their parents to leave them alone together in the same room. Of course, it's not like Karofsky is dumb enough to try anything with adults hovering, but still. Kurt could barely function at the mere thought of Karofsky just months earlier and now he's taking on his bully on his own?
Just look at
Kurt's body language here. This isn't the body language of someone who's afraid. Kurt knows he's the one with the upper hand here. He's leaning forward in his seat (with his hand over his heart at that), putting himself out there. Maybe he's not afraid of Karofsky lashing out or maybe he knows he won't.
And just look at
Karofsky! He clearly wants to be anywhere than where he is right then. He's powerless in this situation and he knows it. He can't even lie to Kurt about Santana; I couldn't have been the only one who was surprised he caved so quickly when Kurt said he owed him and demanded the truth.
Also, did anyone catch Kurt's reaction when Blaine says he'd be okay with Kurt returning to McKinley but for Karofsky?
Kurt's not a happy camper! This is either "I can handle my business!" or "Let's not talk about this, ugh." Could go either way, imo, really. But, given what happened in A Night of Neglect, door number one seems like a real possibility.
I'm running on, like, four hours of sleep so take this as you will.