He bristles, lip twitching once. All this 'please let me worry and take care of you' is just making Jim feel weird. He's not used to it, nor does he find it warranted or necessary. But it seems like if Jim doesn't say yes, Sherr is going to keep this up.
And if he keeps it up, Jim is going to end up in a foul mood. "Fine," he hisses. "Whatever you want. I don't care."