Jeff the Killer #2's Links
Jeff does not really think Mitch is as stupid or incompetent as he makes it seem, he just acts mean like that. While any desire to have companionship is totally latent, he also does not have the impulse to push people away. With Mitch being in the same boat it's a good excuse to stick together. Some part of Jeff likes being around someone who "has it worse", but the other part just kind of likes him.
Mitch can't believe Jeff's audacity and bluntness, and he's at first he's wary -- or at least, in an abstract way /thinks/ he should be a lot more wary than he actually is. Mitch is a little worried about the poor sod, to be honest. What the hell happened to his face, and furthermore, why does he go around killing people?
Push comes to shove, Mitch feels as if they're in the same boat and can't deny that Jeff is the only person who could ever relate to him or see him as more than a monster. (Don't tell him this, but he's also kind of cool.)