Spike has an obligation to protect his partner tooth and nail, and that's all this is about whether that means talking to Jack about what a moron he is or beat the crap out of him when that doesn't work. Whatever it takes. It's the one thing that's always given him some sense of worth in his life, the main reason why he stayed with Dru for so long.
He motions for Jack to hand the bottle over, unscrewing the cork and taking a long pull from it. Fuck. That's better.